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When evaluating shooting incidents to determine if they met the FBI’s active shooter definition, researchers
considered for inclusion:
■ Shootings in public places
■ Shootings occurring at more than one location
■ Shootings where the shooter’s actions were not the result of another criminal act
■ Shootings resulting in a mass killing
■ Shootings indicating apparent spontaneity by the shooter
■ Shootings where the shooter appeared to methodically search for potential victims
■ Shootings that appeared focused on injury to people, not buildings or objects

This report does not encompass all gun-related shootings. Because the risk to civilians in active shooter
incidents appears related to the apparent randomness of so many victims, a gun-related incident was excluded
if research established it was the result of:
■ Self-defense
■ Gang violence
■ Drug violence
■ Contained residential or domestic disputes
■ Controlled barricade/hostage situations
■ Crossfire as a byproduct of another ongoing criminal act
■ An action that appeared not to have put other people in peril (for example, the accidental discharge of a
firearm in a bar or a suicide in a public parking lot)

This methodology was first articulated in A Study of Active Shooter Incidents in the United States Between
2000 and 2013.5

It was applied to 2019 shooting incidents to ensure consistency.