" A 2001 study of adolescent school shooters, prompted in part by the massacre at Columbine High School, resulted in two interesting findings. The first is that 25 percent of the thirty-four teenage shooters they looked at participated in pairs. This is different from adult rampage killers, who most often act alone. Dr. Reid Meloy, a forensic psychologist and expert on targeted violence and threat assessment, authored the study. He told me that these deadly dyads mean it’s absolutely critical for parents to pay attention to the dynamics between kids and their friends. The second finding from his study: typically, one of the two kids was a psychopath, and the other one suggestible, dependent, and depressed. "

― Sue Klebold , A Mother's Reckoning: Living in the Aftermath of Tragedy