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. more