The interactive map below and our downloadable database have been expanded with 18 additional cases from 2013-2016. Back in 2005, the FBI and leading criminologists defined a mass shooting as an 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. In January 2013, a mandate for further federal investigation of mass shootings authorized by President Barack Obama lowered that baseline to three or more victims. 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’ve documented since then using the revised federal baseline reaffirm our major findings.

Mother Jones -Source: A Guide to Mass Shootings in America | Mother Jones