Mass shootings in the United States

There is no fixed definition of a mass shooting in the United States,{{cite news |first=Elyssa |last=Cherney |date=August 5, 2019 |url=https://www.chicagotribune.com/news/ct-cb-mass-shootings-language-definition-gun-violence-20190805-dv2g5lcumbeq3gji4dnycx7j74-story.html |title=The Same Weekend as Massacres in El Paso and Dayton, 15 People Were Shot in 2 Chicago Incidents. Why Aren't Those Called Mass Shootings Too? |work=Chicago Tribune |access-date=August 7, 2019 |quote=Different organizations use a variety of measures to determine whether an act of gun violence meets the criteria of a mass shooting.... How you define the term results in vastly different counts: The Gun Violence Archive has tallied 255 mass shootings in 2019 so far, while Mother Jones lists the number at seven. Some databases also exclude gang-related or domestic shootings.... Researchers on both sides of the spectrum say that data about mass shootings can be misleading if not presented with a clear methodology.}} and different researchers define "mass shootings" in different ways.Jon Greenberg, [https://www.politifact.com/factchecks/2022/may/25/joe-biden/joe-biden-said-mass-shootings-tripled-when-assault Joe Biden said mass shootings tripled when the assault weapon ban ended. They did], PolitiFact (May 25, 2022). Of the 7 following definitions, most use a minimum of 4 victims as a threshold. Among the various definitions are those that are:

• Based on injuries:

:* Gun Violence Archive: More broadly defines "mass shooting" to mean four or more (excluding the perpetrator) shot at roughly the same time and location, regardless of number of fatalities or the motive.{{cite web|title=General Methodology|url=http://www.gunviolencearchive.org/methodology|website=Gun Violence Archive|access-date=February 21, 2018}}{{cite journal |last1=Booty |first1=Marisa |last2=O'Dwyer |first2= Jayne|last3=Webster|first3=Daniel|last4=McCourt |first4=Alex |last5=Crifasi |first5=Cassandra |date=3 Dec 2019 |title=Describing a "mass shooting": the role of databases in understanding burden |journal=Injury Epidemiology |volume=6 |issue=47 |page=47 |doi=10.1186/s40621-019-0226-7 |pmid=31828004 |pmc=6889601 |doi-access=free }}{{cite web|last=Nichols|first=Chris|title=How is a 'mass shooting' defined?|url=https://www.politifact.com/article/2017/oct/04/mass-shooting-what-does-it-mean/|website=PolitiFact California|access-date=February 21, 2018|date=October 4, 2017}} Brady: United Against Gun Violence uses a similar definition.{{cite web|url=https://brady-static.s3.amazonaws.com/Report/MentalHealthImpactOfMassShootings.pdf|title=The Mental Health Impact of Mass Shootings|publisher=Brady: United Against Gun Violence|quote=Brady defines a mass shooting as a shooting incident in which four or more people, other than the shooter, are shot. Brady uses this definition so as not to "exclude, set apart, caveat, or differentiate victims based upon the circumstances in which they were shot."}}

:* Mass Shooting Tracker: Defines "mass shooting" as "an incident where four or more people are shot in a single shooting spree," including the perpetrator or police shootings of civilians around the perpetrator, and irrespective of the motive of the perpetrator or the location of the murders.{{cite web |title=About the Mass Shooting Tracker |url=https://www.massshootingtracker.site/about/ |website=Mass Shooting Tracker |access-date=June 12, 2022}}{{cite web |title=FAQ|url=https://www.massshootingtracker.site/faq/|website=Mass Shooting Tracker |access-date=June 12, 2022}}

• Based on number of deaths:

:* Investigative Assistance for Violent Crimes Act of 2012, signed into law in January 2013: Defines a "mass killing" as the killing of at least three victims, excluding the perpetrator, and regardless of the weapon used.{{cite web|title=H.R. 2076 (112th): Investigative Assistance for Violent Crimes Act of 2012|url=https://www.govtrack.us/congress/bills/112/hr2076/text|website=govtrack.us|publisher=United States Congress|access-date=February 20, 2018|quote=the term mass killings means 3 or more killings in a single incident}}{{cite news|last=Ingraham|first=Christopher|title=What makes a 'mass shooting' in America|url=https://www.washingtonpost.com/news/wonk/wp/2015/12/03/what-makes-a-mass-shooting-in-america/|access-date=November 5, 2017|newspaper=Washington Post|date=December 3, 2015|quote="But starting in 2013, federal statutes defined "mass killing" as three or more people killed, regardless of weapons."}}{{cite web|last=Follman|first=Mark|title=What Exactly Is A Mass Shooting|url=https://www.motherjones.com/mojo/2012/08/what-is-a-mass-shooting|publisher=Mother Jones|access-date=August 9, 2015|quote=In January 2013, a mandate for federal investigation of mass shootings authorized by President Barack Obama lowered that baseline to three or more victims killed.}}

:* Everytown for Gun Safety, which tracks mass shootings based on press accounts, police records, and court papers, defines mass shooting as "any incident in which four or more people are shot and killed, excluding the shooter."{{cite web|url=https://everytownresearch.org/maps/mass-shootings-in-america/|title=Mass Shootings in America |publisher=Everytown for Gun Safety|date=2022}}

• Based on number of deaths and nature of attack:

:* Congressional Research Service (CRS) 2015 report titled Mass Murder with Firearms: Did not define "mass shooting" but defined "public mass shooting" for the purposes of its report as "a multiple homicide incident in which four or more victims are murdered with firearms, within one event, and in one or more locations in close proximity." The CRS further states that its report "attempts to refine the relatively broad concept of mass shooting...into a narrower formulation: public mass shootings."{{cite web|last1=Krouse|first1=William J.|last2=Richardson|first2=Daniel J.|title=Mass Murder with Firearms: Incidents and Victims, 1999–2013| url=https://fas.org/sgp/crs/misc/R44126.pdf| website=FAS.org|publisher=Congressional Research Service|access-date=October 28, 2019|date=July 30, 2015}}

:* Mother Jones's open-source database of mass shootings: The magazine's database, established after the 2012 Aurora movie theater massacre and updated continuously since that time, defines "mass shootings" as "indiscriminate rampages in public places resulting in four or more victims killed by the attacker," excluding "shootings stemming from more conventionally motivated crimes such as armed robbery or gang violence" and shootings in which the perpetrator has not been identified.{{Cite web | url=https://www.motherjones.com/politics/2012/12/mass-shootings-mother-jones-full-data/|title=US Mass Shootings, 1982–2022: Data From Mother Jones' Investigation|publisher=Mother Jones | access-date=June 12, 2022}}{{cite web |url=https://www.motherjones.com/politics/2012/07/mass-shootings-map |title=A Guide to Mass Shootings in America |publisher=Mother Jones|first1=Mark|last1=Follman|first2=Gavin |last2=Aronsen |first3=Deanna |last3=Pan|date= June 9, 2022}} This definition generally is consistent with the FBI's figures and the data used by criminologists.

:* 2022 National Institute of Justice/The Violence Project dataset: Defines "mass public shooting" as an incident in which at least four victims were killed with firearms in a single event "and the murders are not attributable to any other underlying criminal activity or commonplace circumstance (armed robbery, criminal competition, insurance fraud, argument, or romantic triangle)."[https://nij.ojp.gov/topics/articles/public-mass-shootings-database-amasses-details-half-century-us-mass-shootings#note1 Public Mass Shootings: Database Amasses Details of a Half Century of U.S. Mass Shootings with Firearms, Generating Psychosocial Histories], National Institute of Justice/The Violence Project (February 3, 2022).

The FBI defines an "active shooter" incident as "one or more individuals actively engaged in killing or attempting to kill people in a populated area", excluding gun-related incidents that were the result of self-defense, gang or drug violence, residential or domestic disputes, crossfire as a byproduct of another ongoing criminal act, controlled barricade or hostage situations, or actions that appeared not to have put other people in peril.

The appropriateness of a broad versus narrow definition of "mass shooting" has been the subject of debate. Some commentators argue in favor of a narrow definition of mass shootings that excludes the victims of street crime. Mark Follman of Mother Jones, which compiles an open-source database of mass shootings, contends that "While all the victims are important, conflating those many other crimes with indiscriminate slaughter in public venues obscures our understanding of this complicated and growing problem."{{cite news|first=Mark|last=Follman| url=https://www.nytimes.com/2015/12/04/opinion/how-many-mass-shootings-are-there-really.html?_r=1|title=How Many Mass Shootings Are There, Really?|work=The New York Times|date=December 3, 2015|access-date=December 6, 2015}} Northeastern University criminologist James Alan Fox argues against the use of the broad definition of "mass shooting" in the popular press, stating that it misleads readers.{{cite news|first=Elizabeth|last=Stuart|url=http://www.phoenixnewtimes.com/news/number-of-us-mass-shootings-greatly-exaggerated-in-media-acclaimed-researcher-states-7872731|title=Number of U.S. Mass Shootings Greatly Exaggerated in Media, Acclaimed Researcher States|work=Phoenix New Times|date=December 7, 2015|access-date=December 10, 2015}} Others, by contrast, argue that defining "mass shooting" solely as a shooting in a public place in which the perpetrator fires at random is too narrow.{{cite news|author=Mark Hay|url=https://www.vice.com/en/article/8gegkx/what-makes-a-shooting-a-mass-shooting|title=What Makes a Shooting a Mass Shooting?|date=August 29, 2016|work=Vice}} For example, Mark Hay argues that although gang, party, and domestic violence "probably warrant different solutions" than random mass public shootings, a narrow definition fails "to capture and convey the full scope of large-scale gun violence in the United States" and its effect on marginalized communities.

File:1998- Mass shootings in developed countries - bubble chart.svg

File:2000- Outcomes of active shooter attacks (stacked bar chart).svg attacks varied with actions of the attacker, the police (42% of total incidents), and bystanders (including a "good guy with a gun" outcome in 5.1% of total incidents).{{cite news |last1=Buchanan |first1=Larry |last2=Leatherby |first2=Lauren |title=Who Stops a 'Bad Guy With a Gun'? |url=https://www.nytimes.com/interactive/2022/06/22/us/shootings-police-response-uvalde-buffalo.html |work=The New York Times |date=June 22, 2022 |archive-url=https://web.archive.org/web/20220622111531/https://www.nytimes.com/interactive/2022/06/22/us/shootings-police-response-uvalde-buffalo.html |archive-date=June 22, 2022 |quote=Data source: Advanced Law Enforcement Rapid Response Training Center |url-status=live }}]]

{{Map of mass shootings in the United States by death toll}}

{{Map of United States mass shootings/2024}}

As of 2017, studies indicated that the rate at which public mass shootings occur has tripled since 2011. Between 1982 and 2011, a mass shooting occurred roughly once every 200 days. However, between 2011 and 2014, that rate has accelerated greatly with at least one mass shooting occurring every 64 days in the United States.{{Cite news|first1=Amy P. |last1=Cohen|first2=Deborah|last2=Azrael|first3=Matthew|last3=Miller |url=https://www.motherjones.com/politics/2014/10/mass-shootings-increasing-harvard-research/#|title=Rate of mass shootings has tripled since 2011, new research from Harvard shows|work=Mother Jones|date=October 15, 2014|access-date=December 13, 2017|language=en-US}}

Under the definition used by the Gun Violence Archive, by the end of 2019, there were 417 mass shootings; by the end of 2020, there had been 611; and by the end of 2021, 693.{{Cite web| title = Past Summary Ledgers |series=Gun Violence Archive |date=May 13, 2022 | access-date = May 15, 2022 | url = https://www.gunviolencearchive.org/past-tolls}} By mid-May 2021, there were 10 mass shootings per week on average; by mid-May 2022, there was a total of 198 mass shootings in the first 19 weeks of the year, which represents 11 mass shootings a week.{{Cite news| last = Ahmed| first = Saeed| title = It's 19 weeks into the year and America has already seen 198 mass shootings| work = NPR| access-date = May 15, 2022 | date = May 15, 2022 | url = https://www.npr.org/2022/05/15/1099008586/mass-shootings-us-2022-tally-number}} The FBI designated 61 active shooter incidents.{{cite press release|title=FBI Designates 61 Active Shooter Incidents in 2021 |url=https://www.fbi.gov/news/press-releases/press-releases/fbi-designates-61-active-shooter-incidents-in-2021|publisher=FBI National Press Office |access-date=3 June 2022 |format=Press Release |date=23 May 2022}} There were ten mass shootings in 2019, two in 2020, and six in 2021.{{cite web | url=https://www.statista.com/statistics/811487/number-of-mass-shootings-in-the-us/ | title=Number of mass shootings in the U.S. 1982-2022 }} Under the substantially narrower 2022 National Institute of Justice/The Violence Project dataset definition, there were 167 mass shootings (4 or more killed with firearms in public, not connected to "underlying criminal activity or commonplace circumstance") in the U.S. from 1966 to 2019, and 30.8% of the shootings occurred at the workplace.

In 2014, the FBI conducted a review of 160 active shooter incidents in the U.S. from 2000 to 2013 (averaging approximately 11 cases annually) in 40 states and the District of Columbia. The study found that 45.6% took place in a business or commercial setting, 16.9% occurred in schools, 7.5% in institutions of higher education, 9.4% in open spaces, 6.9% in (non-military) government properties, 3.1% in military sites, 4.4% in homes, 3.8% in places of worship, and 2.5% in healthcare settings.{{cite report|last1=Blair|first1=J. Pete|last2=Schweit|first2=Katherine W.|year=2014|title=A Study of Active Shooter Incidents, 2000–2013|publisher=Texas State University/Federal Bureau of Investigation, U.S. Justice Department|place=Washington, D.C.|url=https://www.fbi.gov/file-repository/active-shooter-study-2000-2013-1.pdf/view|access-date=August 18, 2021}} FBI data shows that active shooter incidents increased from 2000 to 2019.

A comprehensive report by USA Today tracked all mass killings from 2006 through 2017 in which the perpetrator willfully killed four or more people. For mass killings by firearm for instance, it found 271 incidents with a total of 1,358 victims.{{cite news|title=Behind the Bloodshed|url=http://www.gannett-cdn.com/GDContent/mass-killings/index.html|work=USA Today|access-date=December 3, 2015}}

In October 2018, PLOS One published a study analyzing 100 mass shootings from the Mother Jones database from January 1982 to May 2018 to evaluate whether mass shootings became more common in the United States over the preceding three decades. It found that mass shootings had steadily increased.{{cite journal|last1=Lin|first1=Ping-I|last2=Fei|first2=Lin|last3=Barzman|first3=Drew|last4=Hossain|first4=M.|year=2018|title=What have we learned from the time trend of mass shootings in the U.S.?|journal=PLOS One|publisher=PLOS|volume=13|issue=10|page=e0204722|doi=10.1371/journal.pone.0204722|pmid=30335790 |pmc=6193640 |bibcode=2018PLoSO..1304722L |doi-access=free}} However, some researchers dispute whether the frequency of mass shootings is increasing due to differences in research methods and differences in the criteria used to define events as mass shootings.{{cite news|last=Kaste|first=Martin|date=March 15, 2018|title=Despite Heightened Fear Of School Shootings, It's Not A Growing Epidemic|work=Morning Edition|publisher=NPR|url=https://www.npr.org/2018/03/15/593831564/the-disconnect-between-perceived-danger-in-u-s-schools-and-reality|access-date=December 2, 2022}}

In 2018 The Washington Post recorded 163 mass shootings in the United States between 1967 and June 2019.{{cite news|url=https://www.washingtonpost.com/graphics/2018/national/mass-shootings-in-america/|title=The terrible numbers that grow with each mass shooting|last1=Berkowitz|first1=Bonnie|newspaper=Washington Post|access-date=November 5, 2017|last2=Gamio|first2=Lazaro|last3=Lu|first3=Denise|last4=Uhrmacher|first4=Kevin|last5=Lindeman|first5=Todd}} Mother Jones recorded 140 mass shootings between 1982 and February 2023.{{Cite web |last1=Follman |first1=Mark |last2=Aronsen |first2=Gavin |last3=Pan |first3=Deanna |title=US mass shootings, 1982–2022: Data from Mother Jones' investigation |url=https://www.motherjones.com/politics/2012/12/mass-shootings-mother-jones-full-data/ |access-date=2022-08-05 |website=Mother Jones |language=en-US}}

Under the Everytown for Gun Safety definition ("any incident in which four or more people are shot and killed, excluding the shooter") there were an average of 19 mass shootings in the U.S. each year from 2009 to 2020, with 947 wounded by gunfire and 1,363 fatally shot. The report found that: "In nearly all mass shootings over this period, the shooter was an adult man who acted alone. Thirty-two percent of mass shooters, or 92 shooters, ended with the perpetrator committing suicide, and another 24 shooters were killed by responding law enforcement. The remaining 145 mass shooters were taken into custody by law enforcement, while the outcomes and identities of 23 remain unknown." In 2022, the Violence Project of the National Institute of Justice recorded 185 mass shootings from 1966 to December 2022.{{Cite web |title=Most Comprehensive Mass Shooter Database |url=https://www.theviolenceproject.org/mass-shooter-database/ |access-date=2022-12-24 |website=The Violence Project |language=en-US}} A 2023 report published in JAMA covering 2014 to 2022, found there had been 4,011 mass shootings in the US.{{Cite journal |last1=Barnard |first1=Leslie M. |last2=Wright-Kelly |first2=Erin |last3=Brooks-Russell |first3=Ashley |last4=Betz |first4=Marian E. |date=2023-07-26 |title=Characterization of Mass Shootings by State, 2014-2022 |journal=JAMA Network Open |volume=6 |issue=7 |pages=e2325868 |doi=10.1001/jamanetworkopen.2023.25868 |pmid=37494046 |issn=2574-3805|pmc=10372703 }}

The 2023 JAMA report showed mass shootings were most frequent around the southeastern U.S. and Illinois. This was true for mass shootings that were crime-, social-, and domestic violence-related. However mass shootings that did not fit any of these categories were geographically distributed more evenly across the U.S. The highest rate was found in the District of Columbia (10.4 shootings per one million people), followed by much lower rates in Louisiana (4.2 mass shootings per million) and Illinois (3.6 mass shootings per million)

{{See also|Lone wolf attack|Aggression#Gender|Sex differences in crime}}

According to The New York Times, there is no common profile of people who carry out mass shootings in the United States, except that they are mostly men.{{cite news|last=Victor|first=Daniel| date=February 17, 2018|url=https://www.nytimes.com/2018/02/17/us/mass-murderers.html|title=Mass Shooters Are All Different. Except for One Thing: Most Are Men|work=The New York Times|access-date=April 10, 2018 |quote=About the only thing almost all of them have in common is that they are men. [...] Examining past New York Times coverage of mass shootings reveals some shared tendencies of the gunmen, including the fact that they are most commonly white}} By race, according to a study, the proportion of mass shooters in the United States who are white is about equal to the overall proportion of white people in the general population of the US.{{Cite web |author=Statista Research Department |date=March 2, 2022 |title=Mass shootings by shooter's race in the U.S. 2021 |url=https://www.statista.com/statistics/476456/mass-shootings-in-the-us-by-shooter-s-race/ |access-date=May 15, 2022 |work=Statista}} The proportion of male mass shooters is considerably larger than the proportion of males in the general population.{{Cite web|url=https://slate.com/news-and-politics/2017/10/what-the-white-mass-shooter-myth-gets-right-and-wrong-about-killers-demographics.html|title=What the White Mass-Shooter Myth Gets Right and Wrong About Killers' Demographics|last=Engber|first=Daniel|date=October 6, 2017|website=Slate Magazine|language=en|access-date=August 4, 2019|quote="roughly 70 percent of the shooters in mass killings were white—certainly a majority. But according to Census Bureau estimates for 2012, whites accounted for 73.9 percent of all Americans" "men are even more overrepresented among mass shooters and mass killers than they are among "normal" killers"}} According to the Associated Press, white men comprise nearly 50% of all mass shooters in the US.{{cite web |title=Mass shootings so far this year almost reach 2018 levels |url=https://apnews.com/article/a027b328810d4a1cab100459b6033ecb |website=AP NEWS |access-date=26 March 2021 |date=8 August 2019|quote="The AP/USA Today/Northeastern database shows that many mass shootings are committed by a certain demographic: young, white men. Most mass shootings in the U.S. are carried out by men, with white men making up nearly 50% of the shooters, the database shows."}} According to the National Institute of Justice/The Violence project study, the demographics of shooters were 97.7% male, with an average age of 34.1 years, 52.3% white, 20.9% black, 8.1% Latino, 6.4% Asian, 4.2% middle eastern, and 1.8% native American.

According to the Center for Inquiry, mass shootings of family members (the most common) are usually carried out by white, middle-aged males. Felony-related mass shootings (connected with a previous crime) tend to be committed by young Black or Hispanic males with extensive criminal records, typically against people of the same ethnic group. Public mass shootings of persons unrelated to the shooter, and for a reason not connected with a previous crime (the rarest but most publicized) are committed by men whose racial distribution closely matches that of the nation as a whole.{{cite web | url =https://centerforinquiry.org/blog/who-are-mass-shooters-mass-shooter-demographics-part-2/ | title =Who Are Mass Shooters? Mass Shooter Demographics | last =Radford | first =Benjamin | date =31 May 2019 | website =Center for Inquiry | access-date =30 March 2021 | quote =The topic of mass shootings is fraught not only with political agendas but also with rampant misinformation. Facile comparisons and snarky memes dominate social media, crowding out objective, evidence-based evidence and analysis. This is effective for scoring political points but wholly counterproductive for understanding the nature of the problem and its broader issues.}}{{cite web |last1=Engber |first1=Daniel |title=What the white mass-shooter myth gets right and wrong about killers' demographics. |url=https://slate.com/news-and-politics/2017/10/what-the-white-mass-shooter-myth-gets-right-and-wrong-about-killers-demographics.html |website=Slate Magazine |publisher=The Slate Group |date=6 October 2017 |access-date=5 January 2022 |quote=that figure, too, wasn't that far off from U.S. demographics}} Other than gender, the demographic profiles of public mass shooters are too varied to draw firm conclusions. In its 2014 active shooter incidents review, the FBI found that the perpetrator was female in only 6 of the 160 incidents (4%) and that in only 2 incidents (1%) was there more than one perpetrator. Analogously, in December 2013, the Journal of Forensic Sciences published a sociodemographic network characteristics and antecedent behaviors survey of 119 lone-actor terrorists in the United States and Europe that found that 96.6% were male.{{cite journal|last1=Gill|first1=Paul|last2=Horgan|first2=John|last3=Deckert|first3=Paige|year=2014|title=Bombing Alone: Tracing the Motivations and Antecedent Behaviors of Lone-Actor Terrorists|journal=Journal of Forensic Sciences|publisher=Wiley-Blackwell|volume=59|issue=2|pages=425–435|doi=10.1111/1556-4029.12312|pmid=24313297 |pmc=4217375 }}

{{See also|Gun culture in the United States|Gun law in the United States|Gun laws in the United States by state|Gun politics in the United States|Gun violence in the United States}}

{{multiple image |total_width=450

| image1= 1970- Gun production - US.svg |caption1=Annual gun production in the U.S. has increased substantially in the 21st century, after having remained fairly level over preceding decades. By 2023, a majority of U.S. states allowed adults to carry concealed guns in public.{{cite web |last1=Mascia |first1=Jennifer |last2=Brownlee |first2=Chip |title=The Armed Era |url=https://www.thetrace.org/2024/04/columbine-shooting-guns-whats-changed/ |publisher=The Trace |archive-url=https://web.archive.org/web/20240414235456/https://www.thetrace.org/2024/04/columbine-shooting-guns-whats-changed/ |archive-date=April 14, 2024 |date=April 9, 2024 |url-status=live }}

| image2= 2019 Gun ownership rates and gun homicide rates - developed world - scatter plot.svg |caption2= Multiple studies show that where people have easy access to firearms, gun-related deaths tend to be more frequent, including by suicide, homicide and unintentional injuries.{{cite news |last1=Fox |first1=Kara |last2=Shveda |first2=Krystina |last3=Croker |first3=Natalie |last4=Chacon |first4=Marco |title=How US gun culture stacks up with the world |url=https://www.cnn.com/2021/11/26/world/us-gun-culture-world-comparison-intl-cmd/index.html |work=CNN |date=November 26, 2021 |archive-url=https://web.archive.org/web/20211126193406/https://www.cnn.com/2021/11/26/world/us-gun-culture-world-comparison-intl-cmd/index.html |archive-date=November 26, 2021 |url-status=live |quote=CNN's attribution: Developed countries are defined based on the UN classification, which includes 36 countries. Source: Institute for Health Metrics and Evaluation (Global Burden of Disease 2019), Small Arms Survey (Civilian Firearm Holdings 2017)}}

}}

{{multiple image |total_width=450

| image1=1982- Deaths from mass shootings in the U.S - scatterplot and line chart.svg |caption1=Total deaths in U.S. mass shootings since 1982—defined as four or more people shot and killed in one incident, excluding the perpetrator, at a public place, excluding gang-related killings.{{cite web |last1=Follman |first1=Mark |last2=Aronsen |first2=Gavin |last3=Pan |first3=Deanna |title=US Mass Shootings, 1982–2023: Data From Mother Jones' Investigation |url=https://www.motherjones.com/politics/2012/12/mass-shootings-mother-jones-full-data/ |publisher=Mother Jones |access-date=March 31, 2023 |archive-url=https://web.archive.org/web/20230331034144/https://www.motherjones.com/politics/2012/12/mass-shootings-mother-jones-full-data/ |archive-date=March 31, 2023 |url-status=live }}{{cite web |last1=Follman |first1=Mark |last2=Aronsen |first2=Gavin |last3=Pan |first3=Deanna |title=A Guide to Mass Shootings in America |url=https://www.motherjones.com/politics/2012/07/mass-shootings-map/ |publisher=MotherJones.com |archive-url=https://web.archive.org/web/20230310230204/https://www.motherjones.com/politics/2012/07/mass-shootings-map/ |archive-date=March 10, 2023 |date=2012 |quote=Updated March 27, 2023. |url-status=live }} Describes inclusion criteria.

| image2 = 1990- AR-15 production as percentage of guns produced in US.svg

| caption2 = After the 2004 expiration of the Federal Assault Weapons Ban, the firearms industry embraced the AR-15's political and cultural significance for marketing. Almost every major gunmaker produces its own version, with ~16 million Americans owning at least one.{{cite news |last1=Frankel |first1=Todd C. |last2=Boburg |first2=Shawn |last3=Dawsey |first3=Josh |last4=Parker |first4=Ashley |last5=Horton |first5=Alex |title=The gun that divides a nation |url=https://www.washingtonpost.com/nation/interactive/2023/ar-15-america-gun-culture-politics/ |newspaper=The Washington Post |date=27 March 2023 |archive-url=https://web.archive.org/web/20230327153545/https://www.washingtonpost.com/nation/interactive/2023/ar-15-america-gun-culture-politics/ |archive-date=27 March 2023 |url-status=live }} Frankel et al. credit: "Source: National Shooting Sports Foundation and Bureau of Alcohol, Tobacco, Firearms and Explosives." Frankel et al. quote: "The shift began after the 2004 expiration of a federal assault weapons ban that had blocked the sales of many semiautomatic rifles. A handful of manufacturers saw a chance to ride a post-9/11 surge in military glorification while also stoking a desire among new gun owners to personalize their weapons with tactical accessories."

}}

Higher accessibility and ownership of guns has been cited as a reason for the U.S.'s high rate of mass shootings.{{cite news|last=Christensen|first=Jen|title=Why the US has the most mass shootings|url=http://edition.cnn.com/2015/08/27/health/u-s-most-mass-shootings/index.html|work=CNN|access-date=November 6, 2017|date=October 5, 2017}}{{cite news|last=Healy|first=Melissa|title=Why the U.S. is No. 1 – in mass shootings|url=https://www.latimes.com/science/sciencenow/la-sci-sn-united-states-mass-shooting-20150824-story.html|access-date=November 6, 2017|work=Los Angeles Times|date=August 24, 2015}} The U.S. has the highest per-capita gun ownership in the world with 120.5 firearms per 100 people; the second highest is Yemen with 52.8 firearms per 100 people. In a Gallup survey conducted in September and October 2020 of 1,035 randomly selected U.S. adults in all 50 states and the District of Columbia, 30% reported personally owning a firearm and 44% reported living in a household that owned at least one firearm,{{cite news|last=Saad|first=Lydia|date=November 13, 2020|title=What Percentage of Americans Own Guns?|publisher=Gallup|url=https://news.gallup.com/poll/264932/percentage-americans-own-guns.aspx}} while the 2020 United States census enumerated the U.S. adult population to be approximately 258.3 million persons in 126.8 million households and the Gun Violence Archive recorded 610 mass shootings in the United States in the same year.{{cite web|last1=Fry|first1=Richard|last2=Passel|first2=Jeffrey S.|last3=Cohn|first3=D'Vera|date=October 12, 2021|title=U.S. household growth over last decade was the lowest ever recorded|publisher=Pew Research Center|url=https://www.pewresearch.org/short-reads/2021/10/12/u-s-household-growth-over-last-decade-was-the-lowest-ever-recorded/|access-date=February 13, 2024}}{{cite press release|last1=Ogunwole|first1=Stella U.|last2=Rabe|first2=Megan A.|last3=Roberts|first3=Andrew W.|last4=Caplan|first4=Zoe|date=August 12, 2021|title=Adult Population Grew Faster Than Total Population From 2010 to 2020: Population Under Age 18 Declined Last Decade|publisher=United States Census Bureau|url=https://www.census.gov/library/stories/2021/08/united-states-adult-population-grew-faster-than-nations-total-population-from-2010-to-2020.html|access-date=April 25, 2024}}{{cite news|last1=Boschma|first1=Janie|last2=Merrill|first2=Curt|last3=Murphy-Teixidor|first3=John|date=October 4, 2023|title=Mass Shootings in the US Fast Facts|publisher=CNN|url=https://www.cnn.com/2023/01/24/us/mass-shootings-fast-facts/index.html|access-date=February 13, 2024}}

Researchers have found a reduction in the number of mass shooting related homicides while the Federal Assault Weapons Ban (FAWB) was in place from 1994 to 2004, which had banned certain types of semi-automatic rifles, including AR-15s.{{cite journal|last1=DiMaggio|first1=Charles|last2=Avraham|first2=Jacob|last3=Berry|first3=Cherisse|last4=Bukur|first4=Marko|last5=Feldman|first5=Justin|last6=Klein|first6=Michael|last7=Shah|first7=Noor|last8=Tandon|first8=Manish|last9=Frangos|first9=Spiros|year=2019|title=Changes in US mass shooting deaths associated with the 1994-2004 federal assault weapons ban: Analysis of open-source data|journal=The Journal of Trauma and Acute Care Surgery|publisher=Lippincott Williams & Wilkins|volume=86|issue=1|pages=11–19|pmid=30188421|doi=10.1097/TA.0000000000002060}} However, researchers also acknowledged that it was difficult to prove that the ban was the cause of this.{{cite news |last1=Schuppe |first1=Jon |title=What makes the AR-15 so beloved and so reviled |url=https://www.nbcnews.com/news/us-news/ar-15-rifle-mass-shootings-semiautomatic-weapon-rcna84193 |publisher=NBC News |date=May 14, 2023}} Conversely, the RAND Corporation published a review in 2023 of five studies researching the effects of the FAWB and state assault weapons bans on the frequency and lethality of mass shootings and found the evidence to be inconclusive, and the review also evaluated two studies researching the effect of high-capacity magazine bans on reducing the frequency and lethality of mass shootings and found the evidence for an effect to be limited.{{cite report|last=Smart|first=Rosanna|date=January 10, 2023|title=Effects of Assault Weapon and High-Capacity Magazine Bans on Mass Shootings|publisher=RAND Corporation|url=https://www.rand.org/research/gun-policy/analysis/ban-assault-weapons/mass-shootings.html|access-date=February 13, 2024}}{{refn|name=RAND review|{{cite journal|last1=Gius|first1=Mark|year=2015|title=The Impact of State and Federal Assault Weapons Bans on Public Mass Shootings|journal=Applied Economics Letters|publisher=Routledge|volume=22|issue=4|pages=281–284|doi=10.1080/13504851.2014.939367}}{{cite journal|last1=Blau|first1=Benjamin M.|last2=Gorry|first2=Devon H.|last3=Wade|first3=Chip|year=2016|title=Guns, Laws, and Public Shootings in the United States|journal=Applied Economics|publisher=Routledge|volume=48|issue=49|pages=4732–4746|doi=10.1080/00036846.2016.1164821}}{{cite report|last1=Luca|first1=Michael|last2=Malhotra|first2=Deepak|last3=Poliquin|first3=Christopher|year=2016|title=The Impact of Mass Shootings on Gun Policy|place=Boston, MA|publisher=Harvard Business School|docket=16-126|ssrn=2776657|url=https://www.hbs.edu/ris/Publication%20Files/16-126_ce055015-fc1c-4a8c-9a8a-8a9361d808bb.pdf|access-date=February 13, 2024}}{{cite journal|last=Gius|first=Mark|year=2018|title=The Effects of State and Federal Gun Control Laws on School Shootings|journal=Applied Economics Letters|publisher=Routledge|volume=25|issue=5|pages=317–320|doi=10.1080/13504851.2017.1319555}}{{cite journal|last1=Klarevas|first1=Louis|last2=Conner|first2=Andrew|last3=Hemenway|first3=David|year=2019|title=The Effect of Large-Capacity Magazine Bans on High-Fatality Mass Shootings, 1990–2017|journal=American Journal of Public Health|publisher=American Public Health Association|volume=109|issue=12|pages=1754–1761|doi=10.2105/AJPH.2019.305311|pmid=31622147|pmc=6836798}}{{cite journal|last1=Webster|first1=Daniel W.|last2=McCourt|first2=Alexander D.|last3=Crifasi|first3=Cassandra K.|last4=Booty|first4=Marisa D.|last5=Stuart|first5=Elizabeth A.|year=2020|title=Evidence Concerning the Regulation of Firearms Design, Sale, and Carrying on Fatal Mass Shootings in the United States|journal=Criminology & Public Policy|publisher=Wiley|volume=19|issue=1|pages=171–212|doi=10.1111/1745-9133.12487|doi-access=free}}}}

Several types of guns have been used in mass shootings in the United States, including semi-automatic handguns, semi-automatic rifles, revolvers, and shotguns.{{cite news |url=https://psmag.com/news/simple-facts-mass-shootings-arent-simple-72055/|last=Todd|first=Michael|title=The Simple Facts About Mass Shootings Aren't Simple at All|work=Pacific Standard|access-date=August 21, 2018|date=December 23, 2013}} Of the 172 events from 1966 to 2019 classified as mass public shootings (four or more victims killed) in the U.S. by the 2022 National Institute of Justice/The Violence Project dataset, perpetrators used handguns in 77.2% of cases and semi-automatic rifles in 25.1% of cases. An earlier 2016 study by James Alan Fox and Emma E. Fridel similarly concluded that "rather than assault weapons, semiautomatic handguns are the weapons of choice for most mass shooters."{{cite journal|author1=James Alan Fox |author2=Emma E. Fridel |title=The Tenuous Connections Involving Mass Shootings, Mental Illness, and Gun Laws|journal=Violence and Gender|volume=3|number=10|date=2016|pages=14–19|doi=10.1089/vio.2015.0054 }} High-capacity magazines were used in more than half of mass shootings over the four decades up to 2018.{{cite news|last=Fisher|first=Marc|title=The AR-15: 'America's rifle' or illegitimate killing machine?|url=http://wapo.st/2BZXJAh?tid=ss_mail|access-date=May 11, 2018|newspaper=The Washington Post|date=February 15, 2018|quote=...high-capacity magazines have been used in more than half of mass shootings over four decades, according to several studies.}} From 1966 to 2019, approximately 77% of mass shooters in the U.S. legally obtained the firearm used in the attacks.{{cite news|author=Glenn Thrush|date=May 16, 2022|title=What Do Most Mass Shooters Have in Common? They Bought Their Guns Legally.|url=https://www.nytimes.com/2022/05/16/us/politics/legal-gun-purchase-mass-shooting.html|newspaper=New York Times}} Although semi-automatic rifles are used in only 1% of overall shootings in the U.S., they are used in 25% of mass shootings, and (as of 2018) in six of the ten deadliest mass shooting events.{{cite news|title=The facts on mass shootings, guns in the United States|url=http://www.politifact.com/truth-o-meter/article/2018/may/18/facts-mass-shootings-guns-united-states/|access-date=June 11, 2018| work=PolitiFact|date=May 18, 2018}}{{cite news|last=Pearce |first=Matt| title=Mass shootings are getting deadlier. And the latest ones all have something new in common: The AR-15| url=http://www.latimes.com/nation/la-na-ar-15-story.html|access-date=May 11, 2018|work=Los Angeles Times|date=February 14, 2018}}

A study published in PLOS One in 2015 examined mass shootings in the U.S. from 2005 to 2013 (and school shootings in the U.S. from 1998 to 2013). The study authors found that the "state prevalence of firearm ownership is significantly associated with the state incidence of mass killings with firearms, school shootings, and mass shootings."{{cite journal|first1=Sherry |last1=Towers |first2=Andres |last2=Gomez-Lievano |first3=Maryam |last3=Khan |first4=Anuj |last4=Mubayi |first5=Carlos |last5=Castillo-Chavez|title=Contagion in Mass Killings and School Shootings|date=2015|journal=PLOS ONE|volume=1|issue=7|pages=e0117259|doi=10.1371/journal.pone.0117259 |pmid=26135941 |pmc=4489652 |bibcode=2015PLoSO..1017259T |doi-access=free }} Conversely, the October 2018 PLOS One study assessed the impact of state-level gun ownership rates in predicting state-level mass shooting rates and found that state-level gun ownership rates were not statistically significantly associated with the number of mass shootings in each state. The researchers tested the possibility that the relationship between gun ownership and the mass shooting rate was being confounded by gun law permissiveness and found that gun law permissiveness was only nominally correlated with gun ownership and that gun ownership was not statistically associated with the mass shooting rate with or without gun law permissiveness being adjusted.

A 2019 study published in The BMJ conducted a cross-sectional time series study of U.S. states from 1998 to 2015; the study found that "States with more permissive gun laws and greater gun ownership had higher rates of mass shootings, and a growing divide appears to be emerging between restrictive and permissive states."{{cite journal |last1=Reeping |first1=Paul M |last2=Cerdá |first2=Magdalena |last3=Kalesan |first3=Bindu |last4=Wiebe |first4=Douglas J |last5=Galea |first5=Sandro |last6=Branas |first6=Charles C |date=2019 |title=State gun laws, gun ownership, and mass shootings in the US: cross sectional time series |url=https://www.bmj.com/content/364/bmj.l542 |journal=The BMJ |volume=364 |pages=l542 |doi=10.1136/bmj.l542 |pmc=6402045 |pmid=30842105}} The study specifically found that "A 10% increase in state gun ownership was associated with a significant 35.1% (12.7% to 62.7%, P=0.001) higher rate of mass shootings. Partially adjusted regression analyses produced similar results, as did analyses restricted to domestic and non-domestic mass shootings." A 2020 study published in Law and Human Behavior examined the relationship of state guns laws and the incidence and lethality of mass shootings in the U.S. from 1976 to 2018. The study found that "laws requiring permits to purchase a gun are associated with a lower incidence of mass public shootings, and bans on large capacity magazines are associated with fewer fatalities and nonfatal injuries when such events do occur."{{cite journal |last1=Siegel |first1= Michael |last2= Goder-Reiser |first2= Max |last3= Duwe |first3= Grant |last4= Rocque |first4= Michael |last5= Fox |first5= James Alan |last6= Fridel |first6= Emma E. |year=2020 |title=The relation between state gun laws and the incidence and severity of mass public shootings in the United States, 1976–2018 |journal=Law and Human Behavior |publisher=American Psychology–Law Society |volume=44 |issue=5 |pages=347–360 |doi=10.1037/lhb0000378 |pmid= 33090863 |url=https://psycnet.apa.org/record/2020-78672-001}} The study specifically found that large-capacity magazine bans were associated with approximately 38% fewer fatalities and 77% fewer nonfatal injuries when a mass shooting occurred.

{{See also|Red flag law|Person–situation debate|Fundamental attribution error|Controversies about psychiatry#Nature of diagnosis|Classification of mental disorders#Criticism|Gender differences in suicide}}

File:Patrick Purdy Stockton Schoolyard Shooting Delaware County Daily Times January 18, 1989.jpg is removed from the grounds of Cleveland Elementary School following his suicide.]]

A panel of mental health and law enforcement experts has estimated that roughly one-third of acts of mass violence—defined as crimes in which four or more people were killed—since the 1990s were committed by people with a "serious mental illness" (SMI). However, the study emphasized that people with an SMI are responsible for less than 4% of all the violent acts committed in the United States.{{Cite web|last=Vestal|first=Christine|date=August 8, 2019|title=One-Third of Mass Shootings Committed by People With Mental Illness, Study Says|url=https://pew.org/2YJlCHt|publisher=The Pew Charitable Trusts}} The American Psychiatric Association (APA) states that gun violence is a public health crisis and has repeatedly noted that the overwhelming majority of people with mental illness are not violent and "are far more likely to be victims of violent crime than perpetrators of violence."{{Cite web|title=APA Condemns Loss of Life from Gun Violence, Disputes Link to Mental Illness|url=https://www.psychiatry.org/newsroom/news-releases/apa-condemns-loss-of-life-from-gun-violence-disputes-link-to-mental-illness|access-date=2021-12-29|website=www.psychiatry.org}}{{Cite web|title=Statement of APA CEO on Gun Violence and Mental Health|url=https://www.apa.org/news/press/releases/2019/08/gun-violence-mental-health|access-date=2021-12-29|date=August 5, 2019|website=www.apa.org}}

In February 2021, Psychological Medicine published a survey reviewing 14,785 publicly reported murders in English language news worldwide between 1900 and 2019 compiled in a database by psychiatrists at the New York State Psychiatric Institute and the Columbia University Irving Medical Center which found that of the 1,315 personal-cause mass murders (i.e. driven by personal motivations and not occurring within the context of war, state-sponsored or group-sponsored terrorism, gang activity, or organized crime) 11% of mass murderers and 8% of mass shooters had an SMI (e.g. schizophrenia, bipolar disorder, major depressive disorder), that mass shootings have become more common than other forms of mass murder since 1970 (with 73% occurring in the United States alone), and that mass shooters in the U.S. were more likely to have legal histories, to engage in recreational drug use or alcohol abuse, and to display non-psychotic psychiatric or neurologic symptoms.{{cite journal|last1=Brucato|first1=Gary|last2=Appelbaum|first2=Paul S.|author-link2=Paul S. Appelbaum|last3=Hesson|first3=Hannah|last4=Shea|first4=Eileen A.|last5=Dishy|first5=Gabriella|last6=Lee|first6=Kathryn|last7=Pia|first7=Tyler|last8=Syed|first8=Faizan|last9=Villalobos|first9=Alexandra|last10=Wall|first10=Melanie M.|author10-link=Melanie Wall|last11=Lieberman|first11=Jeffrey A.|author-link11=Jeffrey Lieberman|last12=Girgis|first12=Ragy R.|year=2021|title=Psychotic symptoms in mass shootings v. mass murders not involving firearms: findings from the Columbia mass murder database|journal=Psychological Medicine|volume=52 |issue=15 |publisher=Cambridge University Press|pages=1–9|pmid=33595428|doi=10.1017/S0033291721000076|s2cid=231944742|url=https://www.cambridge.org/core/journals/psychological-medicine/article/abs/psychotic-symptoms-in-mass-shootings-v-mass-murders-not-involving-firearms-findings-from-the-columbia-mass-murder-database/50514607ADF1AC2ECEB43369B6153E34#|access-date=August 16, 2021}}{{cite news|last1=Ramsland|first1=Katherine|date=February 26, 2021|title=Is There a Link Between Madness and Mass Murder?|work=Psychology Today|publisher=Sussex Publishers|url=https://www.psychologytoday.com/us/blog/shadow-boxing/202102/is-there-link-between-madness-and-mass-murder|access-date=August 16, 2021}}

In October 2022, the Journal of Forensic Sciences published a subsequent review of 82 mass murders in the Columbia University database that at least partially occurred in academic settings that found that 68% of the mass murder perpetrators and 81% of the mass shooters did not have an SMI and that 46% of the mass shootings surveyed ended with the perpetrator committing suicide, leading the researchers to conclude that "To prevent future mass school shootings, we need to begin to focus on the cultural and social drivers of these types of events... rather than on individual predictors" and that "The findings strongly suggest that focusing on mental illness, particularly psychotic illness, when talking about mass school shooting risks is missing other factors that contribute to the vast majority of cases".{{cite journal|last1=Girgis|first1=Ragy R.|last2=Rogers|first2=Russell Tyler|last3=Hesson|first3=Hannah|last4=Lieberman|first4=Jeffrey A.|last5=Appelbaum|first5=Paul S.|last6=Brucato|first6=Gary|year=2022|title=Mass murders involving firearms and other methods in school, college, and university settings: Findings from the Columbia Mass Murder Database|journal=Journal of Forensic Sciences|publisher=Wiley-Blackwell|volume=68|issue=1|pages=207–211|issn=0022-1198|doi=10.1111/1556-4029.15161|pmid=36303265}}{{cite press release|last=Cantor|first=Carla|title=New Findings from the Columbia Mass Murder Database|date=October 28, 2022|publisher=Columbia University Department of Psychiatry|url=https://www.columbiapsychiatry.org/news/new-findings-columbia-mass-murder-database|access-date=February 13, 2024}} Likewise, in a general research review on mass shootings, researchers at the RAND Corporation have noted that due to mass shootings having low base rates, "policies targeting individuals based on risk factors would result in an extremely high rate of false positives" and that the probability of individuals identified by even the most predictive risk factors to commit a mass shooting is "on the order of one in a million."

In 2018, the FBI Behavioral Analysis Unit released a survey of 63 active shooter cases between 2000 and 2013. It found that 62% of active shooters showed symptoms of mental health disorders, but those symptoms may have been "transient manifestations of behaviors and moods that would not be sufficient to warrant a formal diagnosis of mental illness" and that only one-fourth of active shooters surveyed had a formal diagnosis of any mental health disorder (and a psychotic disorder in only 3 cases). The survey concludes that given the high lifetime prevalence of the symptoms of mental illness among the U.S. population, "formally diagnosed mental illness is not a very specific predictor of violence of any type, let alone targeted violence."{{cite report|last1=Silver|first1=James|last2=Simons|first2=Andre|last3=Craun|first3=Sarah|year=2018|title=A Study of Pre-Attack Behaviors of Active Shooters in the United States Between 2000 and 2013|publisher=Federal Bureau of Investigation, U.S. Justice Department|place=Washington, D.C.|url=https://www.fbi.gov/file-repository/pre-attack-behaviors-of-active-shooters-in-us-2000-2013.pdf/view|access-date=June 5, 2022}} The 2021 National Survey on Drug Use and Health conducted by the Substance Abuse and Mental Health Services Administration estimated that 57.8 million U.S. adults had a mental illness and 14.1 million U.S. adults had an SMI,{{cite web|title=Mental Illness – Statistics|publisher=National Institute of Mental Health|url=https://www.nimh.nih.gov/health/statistics/mental-illness|access-date=February 13, 2024}} while the Gun Violence Archive recorded 690 mass shootings in the United States in the same year. Psychiatrist Ronald W. Pies has suggested that psychopathology should be understood as a three-gradation continuum of mental, behavioral and emotional disturbance with most mass shooters falling into a middle category of "persistent emotional disturbance."{{cite news|last=Pies|first=Ronald W.|date=February 17, 2020|title=Mass Shooters and the Psychopathology Spectrum|work=Psychiatric Times|publisher=MJH Associates|url=https://www.psychiatrictimes.com/view/mass-shooters-and-psychopathology-spectrum|access-date=August 17, 2021}}

In 2022, Psychology, Public Policy, and Law published a study by Jillian Peterson, James Densley, and others, assessing the life history variables of 172 mass shooters from 1966 to 2019. The researchers found that symptoms of psychosis played no role in 69% of mass shootings.{{cite journal|last1=Peterson|first1=Jillian K.|last2=Densley|first2=James A.|last3=Knapp|first3=Kyle|last4=Higgins|first4=Stasia|last5=Jensen|first5=Amanda|year=2022|title=Psychosis and Mass Shootings: A Systematic Examination Using Publicly Available Data|journal=Psychology, Public Policy, and Law|publisher=American Psychological Association|volume=28|issue=2|pages=280–291|doi=10.1037/LAW0000314|s2cid=235565400 }} In the October 2018 PLOS One study, the researchers studied whether state-level SMI rates predicted state-level mass shooting rates and found that state-level SMI rates did not predict state-level mass shooting rates. In 2004, the U.S. Secret Service and the U.S. Department of Education issued a report analyzing 41 school shootings in the United States that found that 78% of the shooters surveyed had histories of suicidal ideation or attempted suicide.{{cite report|last1=Vossekuil|first1=Bryan|last2=Fein|first2=Robert A.|last3=Reddy|first3=Marisa|last4=Borum|first4=Randy|last5=Modzeleski|first5=William|year=2004|title=The Final Report and Findings of the Safe School Initiative: Implications for the Prevention of School Attacks in the United States|publisher=U.S. Secret Service/U.S. Department of Education|url=https://www2.ed.gov/admins/lead/safety/preventingattacksreport.pdf|access-date=June 9, 2022}} In its 2014 active shooter incidents review, the FBI found that 96 of the 160 incidents (60%) ended before police arrived, and in 64 incidents (40%) the shooter committed suicide.

In December 2021, the Journal of Threat Assessment and Management published a study comparing 171 public mass shooters and 63 active shooters in the United States from 1966 to 2019 (using cases compiled in The Violence Project's database) to the general population, homicide offenders, and people who die by suicide.{{cite journal|last1=Lankford|first1=A|last2=Silver|first2=J.|last3=Cox|first3=J.|year=2021|title=An epidemiological analysis of public mass shooters and active shooters: Quantifying key differences between perpetrators and the general population, homicide offenders, and people who die by suicide.|journal=Journal of Threat Assessment and Management|publisher=Association of Threat Assessment Professionals|volume=8|issue=4|pages=125–144|doi=10.1037/tam0000166|s2cid=240508009}} In comparison to the general population, mass shooters were more likely to have a history of mental health issues, to have lifetime thought disorders, and greater lifetime suicidal ideation, while in comparison to general homicide offenders, mass shooters four times more frequently premeditated their homicides, eight times more frequently killed strangers, and were more likely to experience suicidal ideation and commit suicide directly or by cop.{{cite news|last1=Vitelli|first1=Romeo|date=January 31, 2022|title=Can Mass Shootings Be Prevented?|work=Psychology Today|publisher=Sussex Publishers|url=https://www.psychologytoday.com/us/blog/media-spotlight/202201/can-mass-shootings-be-prevented|access-date=June 9, 2022}} In comparison to people who committed suicide, mass shooters were actually more likely to have histories of suicidal ideation and were slightly more likely to premeditate the act.{{cite news|last=Koerth|first=Maggie|date=June 6, 2022|title=Suicide Prevention Could Prevent Mass Shootings|website=FiveThirtyEight|url=https://fivethirtyeight.com/features/suicide-prevention-could-prevent-mass-shootings/|access-date=June 9, 2022}} However, like the APA, the researchers emphasized that having a formal mental health disorder diagnosis is more predictive of being a victim of violence rather than a perpetrator. In 2022, there were 49,449 suicides in the United States (a record high) and the suicide rate in 2022 reached its highest level since 1941 at 14.3 per 100,000 persons,{{cite news |author= |date=August 10, 2023 |title=Suicides in the U.S. reached all-time high in 2022, CDC data shows|url=https://www.nbcnews.com/health/mental-health/cdc-data-finds-suicides-reached-time-high-2022-rcna99327|work=NBC News |agency=Associated Press |location= |access-date=August 11, 2023}}{{cite news|last=Wernau|first=Julie|date=November 29, 2023|title=U.S. Suicides Reached a Record High Last Year|work=The Wall Street Journal|publisher=News Corp|url=https://www.wsj.com/health/healthcare/americans-suicide-highest-level-2022-02eb10ea|access-date=February 13, 2024}} while the Gun Violence Archive recorded 646 mass shootings in the United States in the same year.

In the December 2013 Journal of Forensic Sciences lone-actor terrorists survey, lone-actor attacks were rarely sudden or impulsive and the researchers have subsequently noted that a sizable subset of their subjects took preparations to maximize their chances of death by cop or suicide. Based upon the similarities in premeditation and lifetime suicidal ideation, James Densley has argued, "Many of these mass shootings are angry suicides."{{cite news|last=Koerth|first=Maggie|date=August 22, 2019|title=Can We Prevent Mass Shootings By Preventing Suicide?|website=FiveThirtyEight|url=https://fivethirtyeight.com/features/can-we-prevent-mass-shootings-by-preventing-suicide/|access-date=June 9, 2022}} A 2021 cross-sectional study published in JAMA Network Open examining 170 perpetrators of mass public shootings from 1996 to 2019, found that 44% of mass shooters had leaked their plans prior to committing the act, and that "Leakage was associated with receiving counseling and suicidality, which suggests it may be best characterized as a cry for help from perpetrators prior to their act."{{citation|author=Jillian Peterson |author2=Gina Erickson |author3=Kyle Knapp |author4=James Densley |title=Communication of Intent to Do Harm Preceding Mass Public Shootings in the United States, 1966 to 2019|date=November 4, 2021|url=https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2785799|journal=JAMA Network Open|volume=4|issue=11}} "These findings suggest that leakage is a critical moment for mental health intervention to prevent gun violence."

In 2015, psychiatrists James L. Knoll and George D. Annas noted that considering that mass shootings committed by perpetrators with SMIs amount to less than 1% of all gun-related homicides (and that most gun deaths in the United States are suicides rather than homicides),{{cite news|last=Gramlich|first=John|date=February 3, 2022|title=What the data says about gun deaths in the U.S.|publisher=Pew Research Center|url=https://www.pewresearch.org/fact-tank/2022/02/03/what-the-data-says-about-gun-deaths-in-the-u-s/|access-date=January 21, 2023}} the tendency of most media attention following mass shootings on mental health leads to sociocultural factors being comparatively overlooked.{{cite book|last1=Knoll|first1=James L.|last2=Annas|first2=George D.|editor1-last=Gold|editor1-first=Liza H.|editor2-last=Simon|editor2-first=Robert I.|year=2015|title=Gun Violence and Mental Illness|chapter=4. Mass Shootings and Mental Illness|place=New York|publisher=American Psychiatric Association|pages=91–94|chapter-url=https://psychiatryonline.org/doi/pdf/10.5555/appi.books.9781615371099|isbn=978-1-58562-498-0}} Instead, Knoll and Annas cite research by social psychologists Jean Twenge and W. Keith Campbell on narcissism and social rejection in the personal histories of mass shooters, as well as cognitive scientist Steven Pinker's suggestion in The Better Angels of Our Nature (2011) that further reductions in human violence may be dependent upon reducing human narcissism.{{cite book|last1=Twenge|first1=Jean|last2=Campbell|first2=W. Keith|year=2010|title=The Narcissism Epidemic: Living in the Age of Entitlement|place=New York|publisher=Atria Publishing Group|pages=199–200|isbn=978-1-4165-7599-3}}{{cite book|last=Pinker|first=Steven|year=2011|title=The Better Angels of Our Nature: Why Violence Has Declined|title-link=The Better Angels of Our Nature|place=New York|publisher=Penguin Books|pages=519–521|isbn=978-0-14-312201-2}} Conversely, psychologist Peter F. Langman has argued that while mass shooters follow similar patterns, mass shooters do not fit a single psychological profile and the characterization of mass shooters as "friendless loners" is a stereotype.{{cite book|last=Langman|first=Peter F.|year=2021|title=Warning Signs: Identifying School Shooters Before They Strike|place=Allentown, PA|publisher=Langman Psychological Associates|isbn=978-0-578-92299-7}} Psychiatrist Paul S. Appelbaum argued that the data from the New York State Psychiatric Institute and Columbia University Irving Medical Center database of mass shootings show that "legal problems, substance and alcohol use, and difficulty coping with life events seem more useful foci for prevention [of mass shootings] and policy than an emphasis on serious mental illness."{{cite press release|title=Researchers Issue First Report on Mass Shootings from the Columbia Mass Murder Database|date=February 18, 2021|publisher=Columbia University Irving Medical Center|url=https://www.columbiapsychiatry.org/news/researchers-issue-first-report-mass-shootings-columbia-mass-murder-database|access-date=August 17, 2021}}

In the December 2021 Journal of Threat Assessment and Management study, mass shooters were more likely to be unemployed and be unmarried in comparison to the general population, while in comparison to general homicide offenders, mass shooters were more likely to not be in an intimate relationship. In the December 2013 Journal of Forensic Sciences lone-actor terrorists survey, a wide range of activities and experiences preceded lone actors attacks, many but not all lone-actors were socially isolated, lone-actors regularly engaged in a detectable and observable range of activities with a wider pressure group, social movement, or terrorist organization, and a subset of 106 subjects for whom relationship data was available found that 68.9% had never married or were divorced or separated from their spouse and only 27.7% were reported to have children. British criminologist Peter Squires argued that mass shooters in Europe and the U.S. "tend to be loners with not much social support who strike out at their communities, schools and families", and noted that countries with high gun-ownership rates but greater social capital (such as Norway, Finland, Switzerland, and Israel) have fewer mass killings.{{cite news|last=Dorell|first=Oren|title=In Europe, fewer mass killings due to culture not guns|url=https://www.usatoday.com/story/news/world/2012/12/17/guns-mass-killings-worldwide/1776191/|work=USA Today|date=December 18, 2012|access-date=August 11, 2015}}

Psychologist Jillian Peterson and James Densley co-founded The Violence Project, a National Institute of Justice-funded project in which researchers studied every mass shooting since 1966, and approximately 150 mass shooters, and coded 50 life history variables for each.{{citation|url=https://www.latimes.com/opinion/story/2019-08-04/el-paso-dayton-gilroy-mass-shooters-data|title=Op-Ed: We have studied every mass shooting since 1966. Here's what we've learned about the shooters|newspaper=Los Angeles Times|date=August 4, 2019}}{{cite web|title=Shooting Data & Research|website=The Violence Project|publisher=National Institute of Justice|url=https://www.theviolenceproject.org|access-date=June 9, 2022}}{{cite news|last=Pan|first=Deanna|date=June 3, 2022|title=What drives mass shooters? Grievance, despair, and anger are more likely triggers than mental illness, experts say.|work=The Boston Globe|url=https://www.bostonglobe.com/2022/06/03/nation/what-drives-mass-shooters-grievance-despair-anger-are-more-likely-triggers-than-mental-illness-experts-say/|access-date=June 5, 2022}} Their data suggest that almost all mass shooting perpetrators had four life history variables in common: they had (1) commonly experienced early childhood trauma and exposure to violence; (2) "reached an identifiable crisis point in the weeks or months leading up to the shooting," often linked to a specific grievance; (3) researched previous mass shootings, with many being radicalized through the internet; and (4) obtained the means (firearms) to carry out the plan, with perpetrators obtaining weapons from family members in 80% of school shootings, workplace shooters tending to use legally owned handguns, and other public shooters being more likely to acquire firearms illegally. The Violence Project's comprehensive mass shooting database also showed that mass shootings tend to occur in clusters,{{Cite news|url=https://www.wsj.com/articles/indianapolis-shooting-fedex-11618580801|title = Indianapolis FedEx Shooting: Brandon Hole, the Victims, What We Know|newspaper = Wall Street Journal|date = April 17, 2021|last1 = Derosa|first1 = Anthony}} that mass shooters share a sense of entitlement and seek scapegoats when they fail to achieve goals in life, and that hate-motivated and fame-seeking mass shootings have increased since 2015.{{cite web|title=Key Findings - Comprehensive Mass Shooter Data|website=The Violence Project|publisher=National Institute of Justice|url=https://www.theviolenceproject.org/mass-shooter-database-3/key-findings/|access-date=June 10, 2022}} A 2021 article in the journal Injury Epidemiology found that from 2014 to 2019, 59.1% of mass shootings in the United States were related to domestic violence (DV), and the shooter either killed a family member or had a DV history in 68.2% of mass shootings.{{Cite journal |last1=Geller |first1=Lisa B. |last2=Booty |first2=Marisa |last3=Crifasi |first3=Cassandra K. |date=May 31, 2021 |title=The role of domestic violence in fatal mass shootings in the United States, 2014–2019 |journal=Injury Epidemiology |volume=8 |issue=1 |page=38 |doi=10.1186/s40621-021-00330-0 |pmid=34053458 |pmc=8165999 |issn=2197-1714 |doi-access=free }}

Mass shooting contagion (the "copycat phenomenon") has been studied. A study published in PLOS One in 2015 examined mass shootings in the U.S. from 2005 to 2013 (and school shootings in the U.S. from 1998 to 2013). The study authors found that "significant evidence that mass killings involving firearms are incentivized by similar events in the immediate past," concluding that: "On average, this temporary increase in probability lasts 13 days, and each incident incites at least 0.30 new incidents (p = 0.0015). We also find significant evidence of contagion in school shootings, for which an incident is contagious for an average of 13 days and incites an average of at least 0.22 new incidents (p = 0.0001)." The October 2018 PLOS One study found that state-level poverty rates and state-level population sizes did not predict state-level mass shooting rates, but did find that greater online media coverage and online search interest levels correlated with shorter intervals between any two consecutive incidents of mass shootings and the researchers concluded that their findings suggest that online media might correlate with an increasing incidence rate of mass shootings. Steven Pinker has also noted that much of the news media in the United States has an editorial policy of "if it bleeds, it leads".{{cite book|last=Pinker|first=Steven|year=2018|title=Enlightenment Now: The Case for Reason, Science, Humanism, and Progress|title-link=Enlightenment Now|publisher=Viking Press|place=New York|pages=39–52|isbn=978-0-525-42757-5}}

Other posited factors contributing to the prevalence of mass shootings include perpetrators' desire to seek revenge for perceived school or workplace bullying,{{cite journal|last1=Burgess| first1=Ann Wolbert|first2=Christina|last2=Garbarino|first3=Mary I. |last3=Carlson| title=Pathological teasing and bullying turned deadly: Shooters and suicide|journal=Victims and Offenders|volume=1|issue=1|date=2006|pages= 1–14| doi=10.1080/15564880500498705| s2cid=144987837}} the widespread chronic gap between people's expectations for themselves and their actual achievement, perpetrators' desire for fame and notoriety, toxic masculinity (mass shootings are perpetrated almost exclusively by men and boys),{{Cite web |last=Reese |first=Phillip |date=2019-10-07 |title=When masculinity turns 'toxic': A gender profile of mass shootings |url=https://www.latimes.com/science/story/2019-10-07/mass-shootings-toxic-masculinity |access-date=2022-06-25 |website=Los Angeles Times |language=en-US}} and a failure of government background checks due to incomplete databases and/or staff shortages.{{cite news|last=Johnson| first=Kevin|title=Texas Church Shooting Background Check Failure|work=USA Today|date=November 9, 2017|access-date=November 17, 2017|url=https://www.usatoday.com/story/news/politics/2017/11/09/texas-church-shooting-background-check-breakdown-highlights-federal-gun-record-problems/847947001/}}{{cite news|last=Barrett |first=Devlin|title=FBI's Gun Background Check Database Missing Records|work=Chicago Tribune|date=November 10, 2017| access-date=November 17, 2017|url=http://www.chicagotribune.com/news/nationworld/ct-fbi-gun-background-check-system-missing-records-20171110-story.html}} Feminist activist and psychotherapist Harriet Fraad and Marxian economist Richard D. Wolff contend that "American hyper-capitalism" fosters loneliness and social alienation among American men who become mass shooters.{{cite news |last1= Wolff|first1=Richard D.|last2= Fraad|first2=Harriet|date=November 8, 2017 |title=American hyper-capitalism breeds the lonely, alienated men who become mass killers|url=https://www.salon.com/2017/11/08/american-hyper-capitalism-breeds-the-lonely-alienated-men-who-become-mass-killers_partner/|work=Salon |access-date=August 5, 2019|author-link1=Richard D. Wolff|author-link2=Harriet Fraad}} A 2019 analysis of mass shootings from 1990 to 2015 published in BMC Public Health found that communities with rising levels of income inequality are at an increased risk of mass shootings.{{cite journal |last1=Kwon |first1=Roy |last2=Cabrera |first2=Joseph F. |date=September 20, 2019 |title=Income inequality and mass shootings in the United States|journal=BMC Public Health|volume=19 |issue= 1|page=1147 |doi=10.1186/s12889-019-7490-x|pmid=31537201 |quote=There is strong evidence in this study to suggest the recent growth of income inequality is significantly associated with mass shootings in the United States. Specifically, this evidence indicates that a one standard deviation increase in the growth of income inequality augments the number of mass shootings by 0.43 to 0.57.|pmc=6753615 |doi-access=free }}

A British Journal of Political Science study first published in 2017 (and in print in 2019) found that increase in proximity to mass public shootings in the U.S. was associated with statistically significant and "substantively meaningful" increases in support for stricter gun control laws.{{cite journal|title=Mass Shootings and Public Support for Gun Control|journal=British Journal of Political Science|first1=Benjamin J. |last1=Newman |first2=Todd K. |last2=Hartman|pages=1527–1553|volume=49|issue=4|date=2019|doi=10.1017/S0007123417000333|doi-access=free}} The study also found that repeated events, magnitude, and recency of mass shootings play a role with "proximity to repeated events, more horrific events and more recent events" increasing "the salience of gun violence, and thus ... support for gun control." However, the study found that the "most powerful effects" in support or opposition to gun control "are driven by variables related to local culture, with pronounced but expected differences emerging between respondents in rural, conservative, and gun-heavy areas and those residing in urban, liberal areas with few firearm stores." A separate 2019 replication study, extending the earlier panel analysis, found no evidence that mass shootings caused a "significant or substantively meaningful main effect" on attitudes toward gun control.{{cite journal|url=https://www.cambridge.org/core/journals/british-journal-of-political-science/article/abs/reexamining-the-effect-of-mass-shootings-on-public-support-for-gun-control/C76D2FAC726664EBA7F0B7DD5A79117D|title=Reexamining the Effect of Mass Shootings on Public Support for Gun Control|journal=British Journal of Political Science|date=2019|volume=49|issue=4|pages=1555–1565|first1=David J|last1=Barney|first2=Brian F|last2=Schaffner|doi=10.1017/S0007123418000352|s2cid=159183682}} However, the study did find evidence that mass shootings "have polarizing effects conditional on partisanship": "That is, Democrats who live near a mass shooting even tend to become more supportive of gun control restrictions, while Republican attitudes shift in the opposite direction." The study authors concluded, "To the extent that mass shootings may affect public opinion, the result is polarizing rather than consensus building."

A 2020 study published in the American Political Science Review using data on school shootings from 2006 to 2018 concluded the incidents had "little to no effect on electoral outcomes in the United States,"{{Cite journal|last1=Hassell|first1=Hans|last2=Holbein|first2=John|last3=Baldwin|first3=Matthew|date=2020|title=Mobilize for Our Lives? School Shootings and Democratic Accountability in U.S. Elections|url=https://www.cambridge.org/core/journals/american-political-science-review/article/abs/mobilize-for-our-lives-school-shootings-and-democratic-accountability-in-us-elections/B16D170011A6ECDF9EDB555476F1FCB4|journal=American Political Science Review|volume=114|issue=4|pages=1375–1385|language=en|doi=10.1017/S0003055420000635|s2cid=225118870}} whereas a 2021 study in the same journal covering a broader time period (1980–2016) found that the vote share of the Democratic Party increased by an average of almost 5 percentage points in counties that had experienced a "rampage-style" school shooting.{{Cite journal|last1=García-Montoya|first1=Laura|last2=Arjona|first2=Ana|last3=Lacombe|first3=Matthew|date=2021|title=Violence and Voting in the United States: How School Shootings Affect Elections|url=https://www.cambridge.org/core/journals/american-political-science-review/article/abs/violence-and-voting-in-the-united-states-how-school-shootings-affect-elections/48D77237C8B89BCA106ED7BAC20CE2E4|journal=American Political Science Review|volume=116 |issue=3 |pages=807–826|language=en|doi=10.1017/S0003055421001179|s2cid=243948104|issn=0003-0554}} Both studies found no increase in voter turnout.

A 2021 study published in PNAS concluded that "mass shootings have a strong impact on the emotions of individuals, but the impact is politicized, limited to individuals living within the town or city where the incident occurs, and fades within a week of the incident."{{Cite journal|author=Patrick Sharkey & Yinzhi Shen|title=The effect of mass shootings on daily emotions is limited by time, geographic proximity, and political affiliation|date=2021|journal=PNAS|volume=118|issue=23|pages=e2100846118 |doi=10.1073/pnas.2100846118 |pmid=34074780 |pmc=8202016 |bibcode=2021PNAS..11800846S |doi-access=free }} The study authors suggested that this phenomenon could help explain why mass shootings in the U.S. have not led to meaningful policy reform efforts.

{{multiple image

| align = right

| total_width = 270

| image1 = Lasvegassignflowers.jpg

| alt1 =

| caption1 = The Welcome to Fabulous Las Vegas sign following the 2017 Las Vegas shootings{{cite news |url = http://www.foxnews.com/us/las-vegas-shooting-at-least-59-dead-in-massacre-trump-calls-act-of-pure-evil |title = Las Vegas shooting: At least 58 dead in massacre Trump calls 'act of pure evil' |first1 = Adam |last1 = Housley |first2 = William |last2 = La Jeunesse |first3 = Jake |last3 = Gibson |first4 = Catherine |last4 = Herridge |first5 = Mike |last5 = Arroyo |first6 = Brooke |last6 = Singman |first7 = Travis |last7 = Fedschun |date = October 2, 2017 |publisher = Fox News |agency = Associated Press |access-date = October 2, 2017}}{{cite news|url=https://www.reviewjournal.com/crime/homicides/california-woman-declared-59th-victim-of-2017-massacre-in-las-vegas-2102779/|title=California woman declared 59th victim of 2017 massacre in Las Vegas|publisher=The Las Vegas Review-Journal|last=Lacanlale|first=Rio|date=August 24, 2020|access-date=August 27, 2020}}{{cite news|url=https://www.reviewjournal.com/crime/shootings/las-vegas-woman-becomes-60th-victim-of-october-2017-mass-shooting-2123456/|title=Las Vegas woman becomes 60th victim of October 2017 mass shooting|publisher=The Las Vegas Review-Journal|last=Lacanlale|first=Rio|date=September 17, 2020|access-date=September 17, 2020}}

| image2 = James Huberty Injured Survivor Des Moines Register 20 July 1984.jpg

| alt2 =

| caption2 = A slightly wounded survivor of the San Ysidro McDonald's massacre, pictured shortly after the incident

| footer =

}}

A review article first published online in 2015 and then printed in January 2017 in the journal Trauma, Violence, & Abuse concluded that "mass shootings are associated with a variety of adverse psychological outcomes in survivors and members of affected communities". It says that, while "the psychological effects of mass shootings on indirectly exposed populations" is less well-understood, "there is evidence that such events lead to at least short-term increases in fears and declines in perceived safety."{{Cite journal|url=https://journals.sagepub.com/doi/10.1177/1524838015591572|author=Sarah R. Lowe & Sandro Galea|journal=Trauma, Violence, & Abuse|title=The Mental Health Consequences of Mass Shootings|date=2017|volume=18|issue=1|pages=62–82|doi=10.1177/1524838015591572|pmid=26084284|s2cid=43451895}} Identified risk factors for adverse psychological outcomes have included, among others, demographics, greater proximity to the attack, acquaintance with victims, and less access to psychosocial resources.

With the aftermath of the shooting being psychological, hospitals should acquire programs or help facilities for their patients. The most vulnerable patients are children and young adults due to the fact that their brains aren't fully developed. The likelihood of them developing PTSD, depression, anxiety, suicidal thoughts, and more, are extraordinarily high.{{Cite journal |last1=Czaja |first1=Matthew P. |last2=Kraus |first2=Chadd K. |last3=Phyo |first3=Su |last4=Olivieri |first4=Patrick |last5=Mederos |first5=Dalier R. |last6=Puente |first6=Ivan |last7=Mohammed |first7=Salman |last8=Berkeley |first8=Ross P. |last9=Slattery |first9=David |last10=Gildea |first10=Thomas H. |last11=Hardman |first11=Claire |last12=Palmer |first12=Brandi |journal=Western Journal of Emergency Medicine|title=Nonfatal Injuries Sustained in Mass Shootings in the US, 2012–2019: Injury Diagnosis Matrix, Incident Context, and Public Health Considerations. |date=2023 |volume=24 |issue=3 |url=https://dx.doi.org/10.5811/westjem.58395 |pages=562|doi=10.5811/westjem.58395 |pmid=37278791 |pmc=10284525 }} Studies show that 12.4% of mass shooting patients were diagnosed with some form of mental illness, most common being PTSD. Men show lower rates of developing PTSD unlike women who show higher rates. Men and women who fit the criteria for PTSD also showed that they gained depression.{{Cite journal |last1=Czaja |first1=Matthew P. |last2=Kraus |first2=Chadd K |last3=Phyo |first3=Su |last4=Olivieri |first4=Patrick |last5=Mederos |first5=Dalier R. |last6=Puente |first6=Ivan |last7=Mohammed |first7=Salman |last8=Berkeley |first8=Ross P. |last9=Slattery |first9=David |last10=Gildea |first10=Thomas H. |last11=Hardman |first11=Claire |last12=Palmer |first12=Brandi |date=May 2023 |title=Nonfatal Injuries Sustained in Mass Shootings in the US, 2012- 2019: Injury Diagnosis Matrix, Incident Context, and Public Health Considerations. |url=https://dx.doi.org/10.5811/westjem.58395 |journal=Original Journal |volume=24 |issue=3 |pages=564|doi=10.5811/westjem.58395 |pmid=37278791 |pmc=10284525 }}

{{Main|List of mass shootings in the United States}}

The following mass shootings are the deadliest to have occurred in modern U.S. history. Only incidents with ten or more fatalities by gunshots, excluding those of the perpetrators, are included. This list starts in 1949, the year in which Howard Unruh committed his shooting, which was the first in modern U.S. history to incur ten or more fatalities.{{cite news|title=Deadliest Mass Shootings in Modern US History Fast Facts|url=https://edition.cnn.com/2013/09/16/us/20-deadliest-mass-shootings-in-u-s-history-fast-facts/index.html|work=CNN|access-date=April 6, 2018|date=April 1, 2018}}

:{{dagger}} Was previously the deadliest mass shooting

{{Portal|Law|Politics|Medicine|United States}}

{{Div col}}

• List of school massacres by death toll
• Gun laws in the United States
• Gun laws in the United States by state
• Gun violence in the United States
• List of rampage killers in the United States
• School shootings in the United States
• List of school shootings in the United States (before 2000)
• List of school shootings in the United States (2000-present)
• Spree killer
• Public opinion on gun control in the United States
• List of mass shootings in the United States in 2025

{{End div col}}

{{reflist|group=fn}}

{{reflist}}

• Oreskes, Naomi, "Furious about Firearms: Outrage, not hope, will move us to prevent gun violence", Scientific American, vol. 329, no. 1 (July/August 2023), p. 96.

{{Wikiquote}}

• {{Cite web |last=Jetter |first=Michael |author2=Jay K. Walker |title=The Effect of Media Coverage on Mass Shootings |url=http://ftp.iza.org/dp11900.pdf |publisher=IZA Institute of Labor Economics |date=October 2018 |ref=none}}
• [https://www.theviolenceproject.org/mass-shooter-database/ Most Comprehensive Mass Shooter Database]—The Violence Project
• {{Cite web |title=Mass Shootings in 2023 {{!}} Gun Violence Archive |url=https://www.gunviolencearchive.org/reports/mass-shooting |website=Gun Violence Archive}}

{{Mass shootings in the United States|state=autocollapse}}

{{Mass shootings in the United States by deaths}}

{{School shootings in the United States}}

{{Firearms}}

Category:Gun violence in the United States