Self- and other-harm in mass shooters: A dual-harm analysis.

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.