Analysis of Mass Shootings

August 20, 2015

Using FBI data and media reports, Everytown for Gun Safety developed an analysis of mass shootings that took place between January 2009 and July 2015. The analysis found that there have been at least 133 mass shootings in the nearly seven-year period. (View animation: The Real Story of Mass Shootings in America).

Amended August 31, 2016.

Analysis of Recent Mass Shootings

Everytown For Gun Safety conducted a comprehensive analysis of every mass shooting between January 2009 and July 2015 that was identifiable through FBI data and media reports. This report describes the 133 mass shootings – almost two per month that occurred in 39 states in the nearly seven-year period. Each description includes the location of the shooting, number of people killed and/or injured, and information on the shooter, gun(s), ammunition, and gun purchase, where available.

Everytown for Gun Safety defines a mass shooting as an incident in which four or more people, not including the shooter, are killed with a gun. The threshold of four deaths derives from a mass murder definition used in an FBI report from 2005. It is the threshold used by the majority of academics and organizations studying mass violence. Everytown reviewed mass shootings in the FBI’s Supplementary Homicide Reports from 2009-2012 and searched the media for further details about these incidents as well as for mass shootings that occurred in 2013–2015.

This survey includes every shooting we identified in which at least four people were murdered with a gun. And the findings reveal a different portrait of mass shootings in America than conventional wisdom might suggest.

Mass Shootings

Mass shootings represent a small share of total U.S. firearm homicides. Less than one percent of gun murder victims recorded by the FBI in 2012 were killed in incidents with four or more victims.

Mass shootings did not follow any clear seasonal patterns; rather they occurred fairly regularly and no more than three months passed without a mass shooting.


Domestic or Family Violence

Whereas 15% of total gun homicide victims in the U.S. between 2008-12 were female, 50% of the victims of mass shootings in this analysis were female.


There was a noteworthy connection between mass shooting incidents and domestic or family violence. In at least 76 of the cases (57%), the shooter killed a current or former spouse or intimate partner or other family member, and in at least 21 incidents the shooter had a prior domestic violence charge.

Under federal law, domestic abuse only prohibits firearm ownership when the perpetrator has been married to the victim, has a child with them, or cohabits with them. In 23 percent of mass shootings in which the perpetrator killed a former or current partner (13 of 56), there was no evidence the pair had ever married or had a child together.


Perpetrators of mass shootings are generally older than perpetrators of gun violence in the U.S. as a whole.

Whereas the median age of known overall gun murderers in the U.S. is 26, the median age of perpetrators of mass shootings was 34.

High-capacity magazines

High-capacity magazines — or assault weapons likely equipped with them — were used in at least 15 of the incidents (11%). These incidents resulted in an average of 13.3 total people shot — 155% more people shot than in other incidents (5.2) — and 7.5 deaths — 47% more deaths than in other incidents (5.1).


Mental Health

Of 133 examined incidents, in only one was there evidence the shooter was prohibited by federal law from possessing guns due to severe mental illness. In 15 other incidents (11 percent), there was there was evidence that concerns about the mental health of the shooter had been brought to the attention of a medical practitioner, school official, or legal authority prior to the shooting.

Role of Prohibited Possessors

Certain categories of people, including felons, certain domestic abusers, and severely mentally ill people are prohibited by federal law from possessing guns. There was sufficient evidence to judge whether the shooter was a prohibited gun possessor in 116 of the 133 incidents (87%). Of those 116 incidents, 44 (38%) involved a prohibited possessor, and 73 (62%) did not.




In 58 of the 133 incidents (44%), the shooter committed suicide during the incident.




Law Enforcement Shot

In 14 of the 133 shootings (10%), law enforcement or military officers were targeted in the shooting or killed or injured responding to it.




Workplace and School Shootings

Five of the 133 shootings (4%) occurred at the shooter’s current or former workplace. Five of the 133 shooting incidents (4%) took place in schools, including primary, secondary, and college campuses.



“Gun-free Zones”

93 of the 133 incidents (70%) took place wholly in private residences. Of the remaining incidents, only 17 (13%) took place in “gun-free zones” (areas where the carrying of concealed guns is prohibited).




Click here to download an appendix of the shootings profiled in this analysis.