Every time a mass shooting occurs, the country talks about mental health.
Some politicians are quick to point to the shooters' disturbed minds. Some news reporters probe for "loner" tendencies or signs of instability.
"Mental illness and hatred pull the trigger. Not the gun," said President Donald Trump on Monday, after two mass shootings in less than 24 hours.
So is mental illness to blame for America's mass shooting problem? Not according to research.
Some mass shooters have a history of schizophrenia or psychosis, but many do not. And most studies of mass shooters have found only a fraction have any mental health issues. Researchers have noted a host of other factors that are stronger predictors of someone becoming a mass shooter: a strong sense of resentment, desire for infamy, copycat study of other shooters, narcissism and access to firearms.
"It's tempting to try to find one simple solution and point the finger at that," said Jeffrey Swanson, a professor in psychiatry and behavioral sciences at Duke University School of Medicine. "The fact that somebody would go out and massacre a bunch of strangers, that's not the act of a healthy mind, but that doesn't mean they have a mental illness."
As mass shootings have become more common in recent years, their connection to mental health has been increasingly investigated by FBI, police departments, forensic psychiatrists, mental illness experts and epidemiologists.
In a 2018 report of active shooters, the Federal Bureau of Investigation found that 25% of active shooters had been diagnosed with a mental illness. And of those diagnosed, only three shooters had been diagnosed with a psychotic disorder. In a 2015 study that examined 235 people who committed or tried to commit mass killings, only 22% could be considered mentally ill.
Looking at the data differently, almost 5% of the U.S. population suffers from a serious mental illness. A study published in the journal Annals of Epidemiology found that "the large majority of people with mental disorders do not engage in violence against others, and that most violent behavior is due to factors other than mental illness."
"We like to think that anyone who kills others is somehow mentally ill," said Phillip Resnick, who served as a forensic psychiatrist in cases including Oklahoma City bomber Timothy McVeigh and Unabomber Ted Kaczynski. "But you have to remember, people kill for all sorts of reasons. They kill for profit or love or greed."
But mental stress and emotional disturbance can play a role in driving shooters. The 2018 FBI study found that shooters typically experienced several stressors in the year before they attack - financial pressures, fights with classmates or co-workers, and substance abuse. And on average, shooters displayed four to five concerning behaviors that those around them could notice - the most frequent being behavior related to mental health, interpersonal conflicts or some sign of violent intent.
"These may be angry, alienated, troubled young men who are marinating in hate for some other group, for example, and have access to this extremely lethal technology," said Swanson. "So to me, saying it's mental illness is a big dodge to not talk about guns."