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Mass Shootings

Mass Shootings and Mental Illness: Which Research Is Right?

Discrepant studies that address prevention show a need for specificity.

Key points

  • Three recent large-scale studies on mass attacks show disparities over the influence of mental illness.
  • Clumping mental illnesses as a unitary condition provides confusing data for prevention efforts.
  • Effective strategies for preventing mass attacks require clarity on those disorders that have an impact.
Photo by K. Ramsland
Photo by K. Ramsland

Anthony McRae’s attack at the Michigan State University in February — an incident in which four or more people were shot — was the 67th mass shooting in 2023. He killed three and wounded five before ending his own life. In 2022, there were more than 600 mass shootings. Some recent incidents resulted only in injuries, but the three headline-grabbing incidents in California this past January totaled 19 dead and 14 wounded in just three days.

The public’s general impression is that serious mental illness plays a significant role in shootings, but research fails to support this. Recent studies still leave us confused.

NTAC Survey

The U.S. Secret Service National Threat Assessment Center (NTAC) just published its findings from a five-year survey of targeted violence (2016-2020). This group considered incidents in which at least three people were injured and included more than just shootings. The research covers 173 total attacks from locations like workplaces, schools, churches, military bases, residential complexes, public transportation, and open spaces.

The report depicts an array of concerning behaviors as attackers escalate toward violence. Among the key findings:

  • Most had exhibited behavior that concerned family members, friends, neighbors, classmates, and co-workers.
  • Many had a history of aggressive behaviors.
  • Grievances motivated 50 percent.
  • Most used firearms, often illegal.
  • One in four subscribed to a conspiracy or hate ideology.
  • Many experienced stressful trigger events, including those related to family/romantic relationships, employment concerns, and legal issues.
  • More than half experienced mental health symptoms prior to or at the time of their attacks. One in four committed suicide.

Breaking down the mental illness category, the NTAC found that 28 percent (n = 51) had experienced psychotic symptoms prior to or at the time of their attacks. The most common symptoms included paranoia (20 percent), delusions (18 percent), and hallucinations (13 percent). At least one-quarter of the attackers had been formally diagnosed with a mental health condition, including depression, anxiety, post-traumatic stress disorder (PTSD), intermittent explosive disorder, schizophrenia, and bipolar disorder.

Key findings were that individuals who displayed an unusual interest in violent topics should elicit concern. Two out of three attackers had engaged in threatening or concerning communications (emails, videos, drawings, verbal statements) prior to their attack. The most recent communication for two-thirds had occurred within 30 days of the attack. For a third, it was on the day of the attack.

The report’s conclusion is that since most of these behaviors are observable and such attacks are rarely spontaneous, a concerted community effort might effectively prevent many of them. Communities just need some tools to address mental health needs, social isolation, substance abuse, and people in crisis.

That 28 percent of mass attackers had psychotic symptoms seems significant. However, in 2022, a psychiatric team concluded that few mass murderers have been psychotic. Instead, they’re largely angry, rigid, and unable to cope with life’s hard knocks.

The Columbia Study

Brucato, Appelbaum, and other researchers at Columbia University published their findings in Psychological Medicine, based on the comprehensive mass-murder database they’d developed. They’d sifted through 14,785 murders described in English in print or online that had occurred between 1900 and 2019, identifying 1,315 cases of “personal-cause” mass murder. That’s a lot more than in the NTAC study. Over half of the killers were Caucasian, and 28 percent were suicidal (about the same as in the NTAC study). Around 65 percent had used guns.

This group noted that vagueness in descriptions of mental-health conditions created a significant challenge for their analysis: The broader the concept, the higher the percentage of attackers that were deemed mentally ill (up to 78 percent in some studies).

When these researchers narrowed their focus to mass shooters, they found that just 8 percent showed evidence of a psychotic disorder. Even when they included mass murder incidents that used explosives, fires, vehicles, poison, or stabbing, just 11 percent manifested such disorders — higher than in the general population but lower than public perception might suggest, and lower than indicated in the NTAC report. Surprisingly, even severe depression showed up in just 10 percent. (It should be noted that these researchers excluded individuals in acute distress, such as those who’d recently lost a job or loved one, but the NTAC report did include them, which likely accounts for some of the discrepancy.)

Gary Brucato, one of the researchers, remarked, "The findings from this potentially definitive study suggest that emphasis on serious mental illness, such as schizophrenia or psychotic mood disorders, as a risk factor for mass shootings is given undue emphasis, leading to public fear and stigmatization." It also directs preventative resources toward the wrong goals.

Psychosis and Mass Shooting

Peterson, et al (2022) also assessed the role of psychosis vs. employment issues, interpersonal conflict, relationship issues, hate, and fame-seeking in 172 mass shooters. Psychosis was not evident in 69 percent of cases and seemed to have played a minor role in 11 percent, a moderate role in 9 percent, and a major role in 11 percent of the remaining 31 percent of cases. This group concluded that access to mental health care might prevent mass shootings in just a small number of cases.

From these studies, it’s difficult to make out just how impactful psychotic symptoms actually are, but perhaps not all of the 20 percent with paranoid thoughts in the NTAC study were psychotic, or were only moderately psychotic. That category seems vague.

In sum, serious psychotic disorders seem only weakly implicated in mass attacks, and focusing preventive resources on “mental illness” might risk missing other influences that must be addressed.


Brucato, G., Appelbaum, P., Hesson, H., Shea, E., Dishy, G., Lee, K., . . . Girgis, R. (2022). Psychotic symptoms in mass shootings v. mass murders not involving firearms: Findings from the Columbia mass murder database. Psychological Medicine, 52(15), 3422-3430. doi:10.1017/S0033291721000076

Peterson, J. K., Densley, J. A., Knapp, K., Higgins, S., & Jensen, A. (2022). Psychosis and mass shootings: A systematic examination using publicly available data. Psychology, Public Policy, and Law, 28(2), 280–291.

National Threat Assessment Center (2023). Mass attacks in public spaces, 2016-2020.…

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