
Everytown for Gun Safety, which tracks mass shootings based on press accounts,
police records, and court papers, defines mass shooting as "any incident in
which four or more people are shot and killed, excluding the shooter."
Congressional Research Service (CRS) 2015 report titled Mass Murder with
Firearms: Did not define "mass shooting" but defined "public mass shooting" for
the purposes of its report as "a multiple homicide incident in which four or
more victims are murdered with firearms, within one event, and in one or more
locations in close proximity."
Mother Jones's open-source database of mass shootings: The magazine's
database, established after the 2012 Aurora movie theater massacre and updated
continuously since that time, defines "mass shootings" as "indiscriminate
rampages in public places resulting in four or more victims killed by the
attacker," excluding "shootings stemming from more conventionally motivated
crimes such as armed robbery or gang violence" and shootings in which the
perpetrator has not been identified. This definition generally is consistent
with the FBI's figures and the data used by criminologists.
2022 National Institute of Justice/The Violence Project dataset: Defines
"mass public shooting" as an incident in which at least four victims were killed
with firearms in a single event "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)."