A Guide to Mass Shootings in America

There have been at least 99 in the past 35 years—and most of the killers got their guns legally.

Editor’s note: In July 2012, in the aftermath of the movie theater massacre in Aurora, Colorado, Mother Jones created the first open-source database documenting mass shootings in the United States. Our research has focused on indiscriminate rampages in public places resulting in four or more victims killed by the attacker. We exclude shootings stemming from more conventional crimes such as armed robbery or gang violence. Other news outlets and researchers have published larger tallies that include a wide range of gun crimes in which four or more people have been either wounded or killed. While those larger datasets of multiple-victim shootings may be useful for studying the broader problem of gun violence, our investigation provides an in-depth look at the distinct phenomenon of mass shootings—from the firearms used to mental health factors and the growing copycat problem. Tracking mass shootings is complex; we believe ours is the most useful approach.

The interactive map below and our downloadable database have been expanded with 37 additional cases from 2013-2018. Dating back to at least 2005, the FBI and leading criminologists essentially defined a mass shooting as a single attack in a public place in which four or more victims were killed. We adopted that baseline when we gathered data in 2012 on three decades worth of cases. (It is important to note that there have been many similar indiscriminate gun rampages—resulting in fewer fatalities—that would otherwise be included in our dataset.) 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. Accordingly, we include attacks dating from January 2013 in which three or more victims died. Our original analysis, which covers cases with four or more victims killed from 1982-2012, follows below. The cases we have documented since then using the revised federal baseline reaffirm our major findings.

It is perhaps too easy to forget how many times this has happened. The horrific massacre at a movie theater in Aurora, Colorado, in July 2012, another at a Sikh temple in Wisconsin that August, another at a manufacturer in Minneapolis that September—and then the unthinkable nightmare at a Connecticut elementary school that December—were some of the latest in an epidemic of such gun violence over the last three-plus decades. Since 1982, there have been at least 99 public mass shootings across the country, with the killings unfolding in 34 states, from Massachusetts to Hawaii. Sixty of these mass shootings have occurred since 2006. An analysis of this database by researchers at Harvard University, further corroborated by a different study from the FBI, determined that mass shootings have tripled in frequency in recent years.

We’ve gathered detailed data on more than three decades worth of cases and mapped them below, including information on the attackers’ profiles, the types of weapons they used, and the number of victims they injured and killed. The following analysis covers our original dataset comprised of 62 cases from 1982-2012.

Weapons: Of the 143 guns possessed by the killers, more than three quarters were obtained legally. The arsenal included dozens of assault weapons and semi-automatic handguns with high-capacity magazines. (See charts below.) Just as a perpetrator used a .40-caliber Glock to slaughter students in Red Lake, Minnesota, in 2005, so too did the one in Aurora, along with an AR-15 assault rifle, when blasting away at his victims in a darkened movie theater. In Newtown, Connecticut, the attacker wielded a .223 Bushmaster semi-automatic assault rifle as he massacred 20 school children and six adults.

The perpetrators: More than half of the cases involved school or workplace shootings (12 and 20, respectively); the other 30 cases took place in locations including shopping malls, restaurants, and religious and government buildings. Forty-four of the killers were white males. Only one was a woman. (See Goleta, Calif., in 2006.) The average age of the killers was 35, though the youngest among them was a mere 11 years old. (See Jonesboro, Ark., in 1998.) A majority were mentally troubled—and many displayed signs of mental health problems before setting out to kill. Explore the map for further details—we do not consider it to be all-inclusive, but based on the criteria we used, we believe that we’ve produced the most comprehensive rundown available on this particular type of violence. (Mass shootings represent only a sliver of America’s overall gun violence.) For the stories of the 151 shooting rampage victims of 2012, click here, and for our groundbreaking investigation into the economic costs of the nation’s gun violence, including mass shootings, click here.

Click on the dots or use the search tool in the top-right corner of the map to go to a specific location. Zoom in to find cases located geographically close together in Colorado, Texas, Wisconsin, and elsewhere. [Editor’s note: The Oct. 1, 2017 mass shooting on the Las Vegas Strip and several other recent attacks have not yet been added to this map; we will be publishing an updated version soon. In the meantime, see our fully updated database here.]

Our focus is on public mass shootings in which the motive appeared to be indiscriminate killing. We used the following criteria to identify cases:

  • The perpetrator took the lives of at least four people. A 2008 FBI report identifies an individual as a mass murderer—versus a spree killer or a serial killer—if he kills four or more people in a single incident (not including himself), typically in a single location. (*In 2013, the US government’s fatality baseline was revised down to three.)
  • The killings were carried out by a lone shooter. (Except in the case of the Columbine massacre and the Westside Middle School killings, which involved two shooters.)
  • The shootings occurred in a public place. (Except in the case of a party on private property in Crandon, Wisconsin, and another in Seattle, where crowds of strangers had gathered.) Crimes primarily related to gang activity or armed robbery are not included, nor are mass killings that took place in private homes (often stemming from domestic violence).
  • Perpetrators who died or were wounded during the attack are not included in the victim counts.
  • We included a handful of cases also known as “spree killings—cases in which the killings occurred in more than one location over a short period of time, that otherwise fit the above criteria.

For more on the thinking behind our criteria, see these two explanatory pieces. Plus: more on the crucial mental illness factor, and on the recent barrage of state laws rolling back gun restrictions across the US. And: Explore the full data set behind our investigation.

Here are two charts detailing the killers’ weapons:

This guide was first published on July 20, 2012. Since then, we’ve updated and expanded it multiple times with additional research and reporting. The analysis and charts above cover the data through 2012 (comprising 62 cases); additional data and analysis on the shooters’ weapons are in this story. Information on 37 additional mass shootings from 2013-2018 is included in our full data set here. For much more of our reporting on mass shootings, gun violence, and gun laws, see our special investigations: America Under the Gun, Newtown: One Year After, and The True Cost of Gun Violence. (Return to intro.)

Additional reporting and production on this project contributed by: Tasneem Raja, Jaeah Lee, Maggie Caldwell, Olivia Exstrum, and AJ Vicens.