The freshman who walked into the high school cafeteria in Marysville, Wash., in 2014 with his father’s .40-caliber Beretta did not fit anyone’s profile of a mass murderer. He was a crack athlete. He embraced his Native American traditions, wearing a headdress at tribal events and offering freshly killed deer to his grandmother. He was popular, so much so that he had just been elected homecoming prince.
He had no history of mental illness — just what several classmates described as an uncharacteristically bad mood that week. It was only after he killed four fellow students and wounded another that the armchair diagnosis of his mental state began.
Blaming mass murder on mental illness is a time-honored impulse, used by law enforcement and politicians alike. “Mental illness and hatred pulls the trigger, not the gun,” President Donald J. Trump said in 2019 in response to mass shootings in El Paso, Texas, and Dayton, Ohio. After a teenage gunman killed 19 children and two teachers at Robb Elementary School in Uvalde, Texas, in May, Gov. Greg Abbott said, “Anybody who shoots somebody else has a mental health challenge. Period.”
Such explanations satisfy a deep longing to understand the incomprehensible. And they appeal to common sense — how could a person who kills indiscriminately be in their right mind?
Yet America’s mass killers fit no single profile and certainly no pattern of insanity — many, if not most, had never been diagnosed with a serious psychiatric disorder. Background checks can prevent someone with a diagnosis of mental illness from acquiring a gun, but psychologists say there is a wide divide between a clinical diagnosis and the type of emotional disturbance that precedes many mass killings.
The real problem, those experts say, is that mental illness is not a useful means to predict violence. About half of all Americans will experience mental health issues at some point in their lives, and the vast majority of people with mental illness do not kill.
“Do you or do you not have a mental health diagnosis?” said Jillian Peterson, a co-founder of the Violence Project, a research center that has compiled a database of mass shootings from 1966 on and studied perpetrators in depth. “In many cases, it doesn’t really matter. It’s not the main driver.”
Instead, many experts have come to focus on warning signs that occur whether or not actual mental illness is present, including marked changes in behavior, demeanor or appearance, uncharacteristic fights or arguments, and telling others of plans for violence, a phenomenon known as “leakage.”
This focus is far from perfect — it can be exceedingly difficult to weed out serious threats from many more that are idle, impetuous or exaggerated. But the warning signs approach has benefits: It can work even when the mental health system does not, and it sidesteps the complaint that blaming mass shootings on mental illness increases negative attitudes and stigma toward those who suffer from it.
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For Dewey Cornell, an education professor at the University of Virginia who helps train schools to conduct behavioral threat assessments, a bellwether case was that of a high school freshman in West Paducah, Ky. In 1997, he brought guns to school disguised as an art project and opened fire, killing three students and wounding five.
The gunman was schizophrenic and severely delusional, but that was not what helped Dr. Cornell develop his model for averting school violence.
Rather, it was that the killer’s mental state had clearly worsened over time, meaning there had been opportunities to intervene. He had been bullied, had made threats to his peers and had turned in an essay about shooting a bully at school.
“There were many, many warning signs and leakages and not a single student came forward and said, ‘Hey, I’m concerned,’” Dr. Cornell said. “It’s a case I use in all of my training programs to show how we can make a difference.”
Dr. Cornell said the mental health system is ill-suited to avert mass violence, because insurance companies limit what conditions they will pay to treat, and the laws governing psychiatric commitment, which can prevent people from acquiring guns, have a narrow definition of mental illness.
“We identify individuals who are threatening to harm someone, but they do not meet the criteria for hospitalization because they don’t have schizophrenia or bipolar disorder and they don’t express imminent intent to carry out their actions,” Dr. Cornell said.
Red flag laws are intended to get around some of those limitations by allowing for the temporary removal of a person’s guns if they are showing signs of dangerousness, regardless of mental illness.
The problem with relying on mental health diagnoses to predict gun violence has become apparent. The Uvalde gunman had no history of diagnosed mental illness. A teenager in Santa Fe, Texas, had never been diagnosed before he was accused of killing 10 schoolmates in 2018, though he has repeatedly been found mentally incompetent to stand trial. More than once, people who would go on to kill have been evaluated and sent on their way.
In some cases, treatment did not avert violence. The man who killed 12 people in a movie theater in Aurora, Colo., in 2012 had been seeing a psychiatrist specializing in schizophrenia.
After the 1999 Columbine High School shooting, also in Colorado, the journalist Dave Cullen deflated many of the myths surrounding the massacre when he revealed that the perpetrators were neither outcasts nor bullied. Rather, he reported, one of the two gunmen was a psychopath, lacking in conscience and empathy but abundant in grandiose ideas, and the other was a suicidal depressive who went along with the plan.
And in Florida, where a jury is hearing testimony before sentencing on what motivated Nikolas Cruz to kill 17 people at a high school in Parkland in 2018, the defense is expected to present evidence beginning this week that Mr. Cruz suffered from a range of troubles, including brain damage, central nervous system abnormalities and cognitive deficits.
But there were warning signs: While Mr. Cruz was still a student, behavioral health professionals had been called to the school repeatedly because he made threats and exhibited disturbing behavior. Two guidance counselors and a sheriff’s deputy had advised that he be forcibly committed for psychiatric evaluation, but no such commitment ever took place.
In Dr. Peterson’s database, more than two-thirds of the perpetrators had some history of mental health concerns, including hospitalization, counseling, psychiatric medication or a previous diagnosis. About 30 percent of the gunmen had some form of psychosis, a category of mental illness that involves difficulty determining reality, and of those, a third killed in direct response to delusions or hallucinations.
But in many cases, the psychosis did not have an influence on their crime, or was only one of several motivating factors. For example, a college student believed that school employees were conspiring against him and had him under surveillance, but turned violent only after failing to get a refund for his tuition.
All of this has prompted some skepticism about the new federal gun law’s allocation of $8.5 billion to expand the country’s mental health care system, especially when the number of mass killers is vanishingly small. “If we were to cure serious mental illnesses, violence would go down by 4 percent,” said Jeffrey Swanson, a sociologist at Duke University.
Dr. Swanson said his research has found that other factors, like drug and alcohol use, are more closely connected to violence. And study after study has shown that the availability of guns has a far stronger link to violence than psychosocial factors.
Perpetrators are driven by a complex array of factors that can include a desire for fame, radicalization on the internet and childhood trauma, and experts say the means of intervention should be just as broad. Potential killers may be in need of a mentor, substance abuse treatment, cognitive support at school, or even help for their parents such as child care and transportation. Attention to social climate, like anti-bullying campaigns and programs that teach students how to recognize and counteract signs of isolation, may also avert violence.
J. Reid Meloy, a forensic psychologist and F.B.I. consultant, said that whether or not they are mentally ill, most mass killers develop a sense of having been wronged and choose a group to blame. “The personal grievance, then, typically leads to the individual deciding that there is only a violent solution to the distress that they’re experiencing,” he said.
Dr. Peterson of the Violence Project has framed perpetrators not as monstrous outsiders but members — and products — of their communities who are often signaling that they need help. She and other experts say that interventions should emphasize respect, dignity and inclusion. Punitive, exclusionary responses like expulsion from school are likely to increase the risk of violence.
Four out of five of the perpetrators in the project’s database, Dr. Peterson said, showed signs of crisis — defined as a period when one’s circumstances overwhelm one’s coping mechanisms, shortly before carrying out their crimes.
Crisis can be triggered or exacerbated by mental illness, but also by loss of a job, a breakup, divorce, death or other events. The mother of the Parkland gunman died three months before he carried out his attack at the high school, from which he had been expelled.
This suggests that potential violence can be averted. In a TEDx talk called “I Was Almost a School Shooter,” a man named Aaron Stark recounted how a friend’s simple invitation to watch a movie helped divert him from his plans. “When someone treats you like a person when you don’t even feel like a human, it’ll change your entire world,” he said.
In interviews with perpetrators, Dr. Peterson said, “We would always ask, is there anything that could have stopped you? And they would always tell us, yes.” She added, “I think one of them said probably anyone could have stopped me, but there was just no one.”
Patricia Mazzei contributed reporting.