Cumulative and co-occurring strains among mass public shooting perpetrators: implications for violence prevention

Mass public shootings represent a significant source of fatal and nonfatal injury in the United States. This study examines patterns of strain among individuals who carried out these events, with attention to the prevalence, co-occurrence, and cumulative burden of stressors.

Data were drawn from a database of mass public shootings in the United States from 1999 to 2024, comprising 171 incidents and 175 perpetrators. Information was collected using a structured, multi-source approach including official records, secondary reports, and triangulated media sources. Eighteen dichotomous indicators of strain were coded. Descriptive statistics assessed prevalence and cumulative strain, and phi coefficients examined pairwise associations.

Perpetrators experienced multiple, overlapping forms of strain (mean = 4.78; SD = 2.78). Psychiatric concerns, job-related difficulties, and interpersonal stressors were most common. Strains frequently co-occurred, with strong associations among interpersonal and psychological factors and between structural stressors and ideological motivations. Most perpetrators experienced multiple concurrent stressors, indicating that these events rarely are preceded by a single, isolated grievance.

Mass public shootings may be better understood as the result of cumulative and co-occurring strains rather than isolated risk factors. Injury and violence prevention efforts may be strengthened by emphasizing patterns of stressors, early identification, and coordinated, systems-level responses, including threat assessment.