Table of contents

Projects and investigations

Here's a short list of projects attempting to count either gun-related casualties and/or mass killing events in America:

image Active Shooter Incidents - Overview
Active Shooter Incidents - Overview | Federal Bureau of Investigation

The FBI gets a lot of criticism for undercounting or miscategorizing mass shooting incidents. But it’s worth having a base definition:

An active shooter is an individual actively engaged in killing or attempting to kill people in a populated area, and recent active shooter incidents have underscored the need for a coordinated response by law enforcement and others to save lives.

image A Study of Active Shooter Incidents in the United States Between 2000 and 2013

This official report is purportedly based off of a dataset of 160 incidents with 486 people killed.

image America Under the Gun
America Under the Gun | Mother Jones

After the 2012 mass shooting in Aurora, Colorado, Mother Jones launched a five-month special investigation focusing on American gun laws and the apparent rise in mass shootings. Their project included an online database of mass shootings from 1982-2012, which they have updated with major shootings through 2015.

image Behind the Bloodshed: The Untold Story of America's Mass Killings

This investigation found that mass killings in America happened “far more often” than what the government reports, and that their circumstances and the weapons used “are far more predictable than many might think.”

One astonishing takeaway from USA Today’s reporting (emphasis added):

While only about 1% of all murders nationally, mass killings still happen frequently. The FBI counted 172 cases of mass killings between 2006 and 2011. That does not include some large states such as Florida, for example. Poor reporting by police agencies to the FBI also means some mass killings were left out, while others that don’t meet the standard were included.

image How Many People Have Been Killed by Guns Since Newtown?

The answer to the simple question in that headline is surprisingly hard to come by. So Slate is collecting data for our crowdsourced interactive.

image The Gun Violence Archive
The Gun Violence Archive | The eponymous non-profit organization

An online archive of gun violence incidents collected from over 1,200 media, government and commercial sources daily in an effort to provide near-real time data about the results of gun violence.

image Mass Shootings in America
Mass Shootings in America | The Stanford Geospatial Center

This database contains U.S. mass shooting incidents – and their associated geospatial data – over a span of five decades.

image List of school shootings in the United States

Unlike with U.S. police-involved homicides, Wikipedia users have not initiated a seperate project for general mass killings in the United States.

An interactive map of American gun violence based off of the The Gun Violence Archive.

Articles and stories

USA TODAY research reveals flaws in mass-killing data | USA TODAY

A rundown of inconsistencies and omissions in the FBI’s voluntary reporting system of mass killings.

FBI Publication on Serial Murder | Federal Bureau of Investigation

This report contains the FBI’s definition for mass murder – a number of murders (four or more) occurring during the same incident, with no distinctive time period between the murders – to distinguish it from serial murders.

A Year of Gun Deaths | Slate

What Slate learned from trying, and failing, to record every death by gun in America since Newtown.

What We Know About Mass Shootings in America in 2015 | VICE

How many mass shootings have occurred in 2015? And how do you define "mass shooting," anyway?

Has the U.S. had 4 mass shootings this year or 353? Estimates vary that much | Los Angeles Times

In the wake of the San Bernadino massacre, why is it that Mother Jones and the crowd-sourced Mass Shooting Tracker database differ so widely?

Here’s Why No One Can Agree on the Number of Mass Shootings | The New Republic

What’s the difference between a “mass shooting” and a “mass killing”?”

Geospatial Center Tracks Mass Shootings: Sandy Hook slayings prompted an interactive data project. | Stanford Alumni Magazine

An interview with Patricia Carbajales and her motivation for creating the Mass Shootings database while at the Stanford Geospatial Center.

Growing Public Support for Gun Rights (2014) | Pew Research Center

Survey Report For the first time in more than two decades of Pew Research Center surveys, there is more support for gun rights than gun control.

There’s been no calendar week without a mass shooting during President Obama’s second term | The Washington Post

A look at how frequently mass shootings occur


U.S. Mass Shootings, 1982-2015

A dataset of two decades compiled after the 2012 Aurora, Colorado theater shootings. After the publication of the project in 2012, the database has been occasionally updated with major shooting events. The spreadsheet also contains a separate sheet categorizing the weapons used in each incident.

  • The attack must have occurred essentially in a single incident, in a public place
  • We excluded crimes of armed robbery, gang violence, or domestic violence in a home, focusing on cases in which the motive appeared to be indiscriminate mass murder
  • The killer, in accordance with the FBI criterion, had to have taken the lives of at least four people.

Mass Shooting Tracker

This wiki of mass shooting data has been maintained by the users of Reddit’s r/GunsAreCool subreddit since 2013.


A mass shooting is when four or more people are shot in an event, or related series of events, likely without a cooling off period.


Data for the Untold Story of America's Mass Killings

Among the datasets listed here, USA Today has the most comprehensive and complex data schemas, with separate JSON files for events and victims.


To analyze mass killings, USA TODAY used the FBI’s definition: 4 or more killed, not including suspects, in an event. The killing may stretch over a day or more and some distance, especially if it includes killings committed in flight or against targeted people. It does not include an extended “cooling-off period” to distinguish this kind of crime from the acts of serial killers.

People killed by guns in America since the Newtown shootings to the end of 2013.

A data project that attempted to record each gun-related death in America. At the end of the year, Slate wrote about why the project failed.


This dataset did not limit its count to mass killings by gun, but any death caused by a gun. Ultimately, they counted roughly 11,000 reported gun deaths in 2013. The Centers for Disease Control and Prevention reported 32,163 deaths.