A mass shooting is a violent crime in which one or more attackers kill or injure multiple individuals simultaneously using a firearm. There is no widely accepted definition of "mass shooting", and different organizations tracking such incidents use different criteria. Mass shootings are often characterized by the indiscriminate targeting of victims in a non-combat setting, and thus the term generally excludes gang violence, shootouts and warfare. Mass shootings may be done for personal and psychological reasons, but have also been used as a terrorist tactic. The perpetrator of an ongoing mass shooting may be referred to as an active shooter.
In the United States, the country with the most mass shootings, the Investigative Assistance for Violent Crimes Act of 2012 defines mass killings as three or more killings in a single incident.[1] A Congressional Research Service report from 2013 specifies four or more killings on indiscriminate victims while excluding violence committed as a means to an end, such as robbery or terrorism.[2] Media outlets such as CNN and some crime violence research groups such as the Gun Violence Archive define mass shootings as involving "four or more shot (injured or killed) in a single incident, at the same general time and location, not including the shooter".[3] Mother Jones magazine defines mass shootings as indiscriminate rampages killing three or more individuals excluding the perpetrator, gang violence, and armed robbery.[4][5] An Australian study from 2006 specifies five individuals killed.[6]
The number of people killed in mass shootings is difficult to determine due to the lack of a commonly agreed definition. In the United States, there were 103 deaths in mass shootings in 2021 (excluding the perpetrators) using the FBI's definition, and 706 deaths using the Gun Violence Archive's definition.[7] The FBI's definition refers to "active shooter incidents" defined as "one or more individuals actively engaged in killing or attempting to kill people in a populated area", while the Gun Violence Archive's definition counts incidents where at least four people (excluding the perpetrator) were shot, but not necessarily killed.[7]
The motive for mass shootings (that occur in public locations) is usually that they are committed by deeply disgruntled individuals who are seeking revenge for failures in school, career, romance, or life in general[8] or who are seeking fame or attention[9] with at least 16 mass shooters since the Columbine massacre citing fame or notoriety as a motive.[10] Fame seekers average more than double the body counts, and many articulated a desire to surpass "past records".[10]