Introduction: Research suggests that individuals engaging in both self- and other-harm (viz., dual-harm) face increased risks of negative outcomes compared to those with single-harm (either self- or other-harm) or no-harm histories. This study examines mass shooters through this lens and compares them across multiple risk factors.
Methods: This study analyzed 197 U.S. mass shooters in public incidents with four or more fatalities (August 1966 to January 2023), using The Violence Project Database. Nearly all were men (97.5 %), with a mean age of 34 (M = 33.97, SD = 12.65, range = 11-72). Participants were categorized into no-harm, single-harm, or dual-harm groups based on histories of thoughts of self-harm, aggression, and violent crime.
Results: One-fifth (n = 40) exhibited dual-harm, with this group showing the highest prevalence of most risk factors. They had significantly more adverse childhood experiences (no-harm = 0.56, single-harm = 1.02, dual-harm = 1.88, p < .001, ε² = .091). Compared to the no-harm group (31.5 %), dual-harm individuals had significantly higher rates of sexual abuse, single-parent upbringing, psychiatric hospitalization, psychiatric medication, prior counseling, mood disorders, drug use, bullying, animal abuse, criminal records, abusive behavior, interest in past mass violence, fame-seeking, video game engagement, and leakage. Compared with the single-harm group, the dual-harm group (48.2 %) had significantly higher rates of sexual abuse and leakage.
Conclusions: Examining mass violence from the trichotomy of harm levels highlights a high-risk subset with complex needs, while also identifying a lower-risk no-harm group, underscoring the heterogeneity of their life experiences and behaviors.
Keywords: Adverse childhood experiences; Firearms; Gun violence; Mass shootings; Mass violence; Suicide.
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