(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.
Accordingly, we include attacks dating from January 2013 in which three or more victims died.
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.
We adopted that baseline when we gathered data in 2012 on three decades worth of cases.
Our original analysis, which covers cases with four or more victims killed from 1982-2012, follows below.
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.
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The interactive map below and our downloadable database have been expanded with 22 additional cases from 2013-2016.
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