We adopted that baseline when we gathered data in 2012 on three decades worth of cases.(It bears noting that there have been many similar indiscriminate gun rampages with 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.The cases we have documented since then using the revised federal baseline reaffirm our major findings. 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.
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.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 interactive map below and our downloadable database have been expanded with 22 additional cases from 2013-2016.
Dating from 2005, the FBI and leading criminologists essentially defined a mass shooting as an attack in a public place in which four or more victims were killed.