Share of mass public shooters U.S. 1999-2024, by location/relation to shooting site

From 1966 to January 2024, all mass public shooters who carried out shootings at a post office or at a warehouse or factory in the United States were considered 'location insiders', as 100 percent were found to have an existing relationship to the shooting site. In contrast, mass shootings which took place in retail locations had a greater chance of being conducted by someone unaffiliated with the location; within the provided time period, 83 percent of mass public shooters behind retail shootings were seen as outsiders to their chosen shooting site. Similarly, the majority of mass public shooters who chose a restaurant, bar, or nightclub as the site of shooting had no existing relationship to these locations, at 79 percent.

The source defines a mass public shooting as: “a multiple homicide incident in which four or more victims are murdered with firearms—not including the offender(s)—within one event, and at least some of the murders occurred in a public location or locations in close geographical proximity (e.g., a workplace, school, restaurant, or other public settings), and the murders are not attributable to any other underlying criminal activity or commonplace circumstance (armed robbery, criminal competition, insurance fraud, argument, or romantic triangle). Mass shootings attributable to gangs, as well as most domestic homicides, are therefore excluded from this definition.