Jillian K. Peterson

Firearm violence is a leading cause of premature death worldwide, and mass public shootings sit at the far tail of severity. Research has linked higher casualty counts to assault weapons, but the category enters those studies as a single yes/no indicator, so the weapon characteristics behind the association remain unidentified. We analyzed 197 US mass public shootings from 1966 through 2025 (202 perpetrators, 433 firearms, 288 fired) recorded in The Violence Project Mass Shooter Database, splitting the assault weapon category into weapon platforms, cartridge energy classes, and magazine capacity. Assault weapon use held between 17 and 20% of incidents per decade from the 1970s through the 2000s, then rose to 36% in the 2010s and 60% in the incomplete 2020s, with the shift concentrated after 2015. In adjusted negative binomial models, assault weapon use was associated with 55% more fatalities and roughly four times as many injuries; excluding the 2017 Las Vegas shooting cut the injury estimate to 2.3. The AR-15 was the only platform associated with both outcomes, but an additive model of platform and cartridge is rejected in favor of an interaction (likelihood ratio P < .05 for both outcomes, with and without the Las Vegas outlier), and neither component carries the association alone. Excluding Las Vegas and adjusting for magazine capacity, incidents in which an AR-15 fired a rifle-class cartridge had 1.6 times the fatalities and 2.4 times the injuries of the reference category, while rifle-class cartridges fired from other platforms showed none. Large-capacity magazines were independently associated with both outcomes, at 1.4 for fatalities and 1.8 for injuries, and the magazine estimate for fatalities moved little across every model we fit. What the binary classification records as one exposure is a compound of platform, ammunition, and magazine capacity, and the components do not behave alike.

Background: Firearm violence in the United States is highly concentrated within specific demographic, economic, geographic, and social population groups. Prior research indicates elevated violence exposure among gang-involved individuals, but the extent and mental health implications of firearm victimization at the national level remain poorly understood. Methods: We analyzed data from a national online survey of 10,000 U.S. adults fielded in 2024. Respondents self-reported lifetime gang membership and lifetime exposure to five forms of firearm victimization: presence at a mass shooting, gun threats, being shot at without injury, accidental gunshot injury, and intentional gunshot injury. Weighted descriptive statistics compared prevalence by lifetime gang status. Multivariable logistic regression estimated adjusted odds ratios controlling for several covariates. Among victims of firearm violence, self-reported psychological impacts, including anxiety, fear, depression, panic attacks, and post-traumatic stress symptoms, were assessed. Results: People with a history of gang involvement reported substantially higher lifetime exposure to all forms of firearm victimization. After adjustment, gang involvement was associated with 2–4 times greater odds of firearm exposure across outcomes. Psychological impacts following firearm victimization were prevalent in both gang and non-gang groups. Differences in reported mental health impacts by gang status were generally modest, with relatively few statistically significant differences in adjusted models. Conclusions: Firearm victimization is highly concentrated among people with a history of gang involvement, and such exposure is associated with substantial psychological distress. Mental health impacts were broadly similar across gang-involved and non-gang victims. These findings highlight the importance of recognizing gang-involved adults as a population with disproportionate exposure to firearm violence and significant trauma-related needs within a public health framework.

This in-depth review delves into the multifaceted realm of mass shootings and explores their epidemiology from a psychological perspective. The article presents a comprehensive examination of the prevalence, perpetrator and victim profiles, motives, and contributing factors associated with mass shootings. By investigating the intricate relationship between masculinity, domestic violence, military service, social media, fame-seeking, suicidal ideation, mental illness, and firearms, this article sheds light on the multifaceted nature of mass shootings. Moreover, it discusses the importance of implementing effective prevention strategies to address this growing public health concern. The findings from this review serve as a valuable resource for researchers, practitioners, policy makers, and the community at large, facilitating a deeper understanding of mass shootings and fostering the development of evidence-based solutions to prevent these tragic incidents.

This mixed-methods study examines social media use among public mass shooters in the United States as an extension of a comprehensive database of 170 mass shooters from 1966 to 2021. Here, we report findings from a systematic content analysis of public data and detailed timelines that were constructed for 44 mass shooters’ social media habits and changes to those habits during the period of time leading up to their shooting. The paper also presents as a case study, a sentiment analysis, and term-linkage network for one perpetrator’s total 3,000 tweets. Several themes were found in the data—there were shooters who changed their posting habits and in some cases, stopped using social media entirely in the lead up to their crime; shooters who used hate speech and were “radicalized” to violence online; shooters with a demonstrable interest in violence, who referenced past mass shooters in their own communications; shooters who exhibited signs of mental illness and suicidality; shooters who were already known to authorities; and shooters who like those described above, actively posted while shooting, presumably to boost their own celebrity status. The findings from this study provide insight into commonalities among mass shooters in terms of their social media usage, which could lead to new pathways for prevention and intervention.

Mass public shootings, an event in which 4 or more people (not including the perpetrator) are killed with firearms in a public space, are a public health crisis.¹ Mass shootings are statistically rare in comparison with other forms of gun violence, but because the perpetrators of mass shootings often have no relationship with their victims, every public space feels vulnerable (eg, schools, concerts, grocery stores, movie theaters, churches), and they require bespoke mitigation.² One promising avenue for mass shooting prevention is threat assessment, which was born out of work by the US Secret Service after several high-profile attacks on public officials and figures.³

After deadly school shootings at Columbine, Sandy Hook, and Parkland, many states mandated School Resource Officers or provided funding for districts to hire them.¹ Lawmakers also considered arming teachers. Florida now requires a law enforcement officer or trained school guardian in every school.²