Are mass murderers insane?

Usually not, researchers say

If what people do is any reflection of who they are, then Devin P. Kelley, who slaughtered 26 churchgoers on Nov. 5 in Texas, surely was a madman.

Before the atrocity, he had attempted to sneak weapons onto an Air Force base after making death threats to his superiors, according to a local police report. In 2012, he had escaped from a mental hospital in New Mexico to which he had been sent after assaulting his wife and fracturing his stepson’s skull.

A video of the church killing reportedly shows Kelley working his way methodically through the aisles, shooting some parishioners, even children, at point-blank range.

“I think that mental health is your problem here,” President Donald Trump told reporters the next day.

It is true that severe mental illnesses are found more often among mass murderers. About one in five are likely psychotic or delusional, according to Dr. Michael Stone, a forensic psychiatrist at Columbia University who maintains a database of 350 mass killers going back more than a century. The figure for the general public is closer to 1 percent.

But the rest of these murderers do not have any severe, diagnosable disorder. Though he was abusive to his wife, Omar Mateen, who killed 49 people in an Orlando nightclub, had no apparent serious mental illness. Neither did Stephen Paddock, who mowed down 58 concertgoers from a hotel window in Las Vegas.

Ditto for Dylann Roof, the racist who murdered nine African-american churchgoers in South Carolina in 2015, and Christopher Harper-mercer, the angry young man who killed nine people at a community college in Oregon the same year.

Nor does anything in these criminals’ history — including domestic violence, like Kelley’s — serve to reliably predict their spectacularly cruel acts. Even if spree killers