PIRUS: Mass Casualty Extremist Offenders with U.S. Military Backgrounds

Beginning in 2021, the Radicalization and Disengagement team at the National Consortium for the Study of Terrorism and Responses to Terrorism (START) at the University of Maryland began an ongoing project to collect comprehensive data on extremist offenders with U.S. military backgrounds. These data serve as an addendum to the Profiles of Individual Radicalization in the United States (PIRUS) database, which includes information on more than 3,000 subjects who committed extremist crimes in the United States. In this research brief, we take a closer look at the subset of U.S. extremist offenders in PIRUS with military backgrounds who plotted to commit, or committed, mass casualty terrorist attacks in the United States from 1990-2022. A mass casualty plot is defined as an event in which the perpetrator(s) intended to injure or kill four or more victims. A successful mass casualty attack is one that resulted in four or more combined victim deaths or injuries, while a successful mass fatality attack is one that resulted in four or more victim deaths. In this brief, we analyze the characteristics that distinguish mass casualty offenders from extremists who engaged in less lethal or non-violent crimes. We also examine how often extremists with military backgrounds plot mass casualty attacks and how often they succeed in causing significant harm. Finally, we review the military branch and ideological affiliations of mass casualty offenders with U.S. military service backgrounds.

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