Mass shooters and mental Illness: Reexamining the connection

MDedge Psychiatry

Publish date: December 5, 2023

By Nina E. Cerfolio, MD  Ira D. Glick, MD

Our psychiatric research, which found a high incidence of undiagnosed mental illness in mass shooters, was recently awarded the esteemed Psychodynamic Psychiatry Journal Prize for best paper published in the last 2 years (2022-2023). The editors noted our integrity in using quantitative data to argue against the common, careless assumption that mass shooters are not mentally ill.

Some of the mass shooters we studied were motivated by religious or political ideologies that were considered forms of terrorism. Given the current tragically violent landscape both at home and in Israel/Palestine, the “desire for destruction” is vital to understand.

Although there have been a limited number of psychiatric studies of perpetrators of mass shootings, our team took the first step to lay the groundwork by conducting a systematic, quantitative study. Our psychiatric research team’s research findings were published in the Journal of Clinical Psychopharmacology and then in greater detail in Psychodynamic Psychiatry,1,2 which provided important context to the complicated backgrounds of these mass shooters who suffer from abuse, marginalization, and severe undiagnosed brain illness.3

The Mother Jones database of 115 mass shootings from 1982 to 2019 was used to study retrospectively 55 shooters in the United States. We developed a uniform, comprehensive, 62-item questionnaire to compile the data collection from multiple sources and record our psychiatric assessments of the assailants, using DSM-5 criteria. After developing this detailed psychiatric assessment questionnaire, psychiatric researchers evaluated the weight and quality of clinical evidence by (1) interviewing forensic psychiatrists who had assessed the assailant following the crime, and/or (2) reviewing court records of psychiatric evaluations conducted during the post crime judicial proceedings to determine the prevalence of psychiatric illness. Rather than accepting diagnoses from forensic psychiatrists and/or court records, our team independently reviewed the clinical data gathered from multiple sources to apply the DSM-5 criteria to diagnose mental illness.

In most incidents in the database, the perpetrator died either during or shortly after the crime. We examined every case (n=35) in which the assailant survived, and criminal proceedings were instituted.

Of the 35 cases in which the assailant survived and criminal proceedings were instituted, there was insufficient information to make a diagnosis in 3 cases. Of the remaining 32 cases in which we had sufficient information, we determined that 87.5% had the following psychiatric diagnosis: 18 assailants (56%) had schizophrenia, while 10 assailants (31%) had other psychiatric diagnoses: 3 had bipolar I disorder, 2 had delusional disorders (persecutory), 2 had personality disorders (1 paranoid, 1 borderline), 2 had substance-related disorders without other psychiatric diagnosis, and 1 had post-traumatic stress disorder (PTSD).

Out of the 32 surviving assailants for whom we have sufficient evidence, 87.5% of perpetrators of mass shootings were diagnosed with major psychiatric illness, and none were treated appropriately with medication at the time of the crime. Four assailants (12.5%) had no psychiatric diagnosis that we could discern. Of the 18 surviving assailants with schizophrenia, no assailant was on antipsychotic medication for the treatment of schizophrenia prior to the crime. Of the 10 surviving assailants with other psychiatric illnesses, no assailant was on antipsychotic and/or appropriate medication.

In addition, we found that the clinical misdiagnosis of early-onset schizophrenia was associated with the worsening of many of these assailants’ psychotic symptoms. Many of our adolescent shooters prior to the massacre had been misdiagnosed with attention-deficit disorder (ADD), major depression disorder (MDD), or autism spectrum disorder.

Though the vast majority of those suffering from psychiatric illnesses who are appropriately treated are not violent, there is a growing body of scientific research that indicates a strong association of untreated brain illness with those who commit mass shootings.4,5,6 This research demonstrates that such untreated illness combined with access to firearms poses a lethal threat to society.

Most of the assailants also experienced profound estrangement, not only from families and friends, but most importantly from themselves. Being marginalized rendered them more vulnerable to their untreated psychiatric illness and to radicalization online, which fostered their violence. While there are complex reasons that a person is not diagnosed, there remains a vital need to decrease the stigma of mental illness to enable those with psychiatric illness to be more respected, less marginalized, and encouraged to receive effective psychiatric treatments.

Dr. Cerfolio is author of “Psychoanalytic and Spiritual Perspectives on Terrorism: Desire for Destruction.” She is clinical assistant professor at the Icahn School of Medicine at Mount Sinai, New York. Dr. Glick is Professor Emeritus, Department of Psychiatry and Behavioral Sciences at Stanford University School of Medicine, Stanford, Calif.


1. Glick ID, et al. Domestic Mass Shooters: The Association With Unmedicated and Untreated Psychiatric Illness. J Clin Psychopharmacol. 2021 Jul-Aug;41(4):366-369. doi: 10.1097/JCP.0000000000001417.

2. Cerfolio NE, et al. A Retrospective Observational Study of Psychosocial Determinants and Psychiatric Diagnoses of Mass Shooters in the United States. Psychodyn Psychiatry. 2022 Fall;50(3):1-16. doi: 10.1521/pdps.2022.50.5.001.

3. Cerfolio NE. The Parkland gunman, a horrific crime, and mental illness. The New York Times. 2022 Oct 14.

4. Corner E, et al. Mental Health Disorders and the Terrorist: A Research Note Probing Selection Effects and Disorder Prevalence. Stud Confl Terror. 2016 Jan;39(6):560–568. doi: 10.1080/1057610X.2015.1120099.

5. Gruenewald J, et al. Distinguishing “Loner” Attacks from Other Domestic Extremist Violence. Criminol Public Policy. 2013 Feb;12(1):65–91. doi: 10.1111/1745-9133.12008.

6. Lankford A. Detecting mental health problems and suicidal motives among terrorists and mass shooters. Crim Behav Ment Health. 2016 Dec;26(5):315-321. doi: 10.1002/cbm.2020.