IMPORTANCEUnderstanding the motivation of a mass shooter's intent to do harm can help practitioners and policy makers develop more effective intervention strategies. OBJECTIVE To examine the prevalence of communication of intent to do harm, known as leakage, in a sample of 170 mass public shooters from 1966 to 2019; the characteristics of perpetrators who do and do not leak their plans; and whether leakage is a form of fame-seeking behavior or a cry for help among individuals who are in crisis or suicidal. DESIGN, SETTING, AND PARTICIPANTS This cross-sectional study included perpetrators who

Mass shootings are often blamed on serious mental illness. This study assesses the role of psychosis in contributing to mass shootings along a continuum. The role of psychosis is compared with other motivations for mass shootings including employment issues, interpersonal conflict, relationship issues, hate, and fame-seeking. Perpetrators motivated by psychosis are also compared with other perpetrators on several well-established risk factors for violence. It is hypothesized that a mental health history is common among mass shooters, but symptoms of psychosis only directly motivate mass shootings for a minority of cases. A dataset of 172 mass shooters was created, coded on 166 life history variables using publicly available data. The entire dataset and codebook are publicly available. The findings show that symptoms of psychosis played no role in 69% of cases, but psychosis may have played a minor role in 11% of cases, a moderate role in 9% of cases, and a major role in 11% of cases. Perpetrators motivated by psychosis were similar to mass shooters with other motivations in terms of demographics and common risk factors for violence. The role of serious mental illness in mass shootings is complex. The data indicate that access to mental health care may help prevent mass shootings in a minority of cases, but this is far from the only solution to mass shootings.

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