"Fuselier and Ochberg say that if you want to understand “the killers,” quit asking what drove them. Eric Harris and Dylan Klebold were radically different individuals, with vastly different motives and opposite mental conditions. Klebold is easier to comprehend, a more familiar type. He was hotheaded, but depressive and suicidal. He blamed himself for his problems. Harris is the challenge. He was sweet-faced and well-spoken. Adults, and even some other kids, described him as “nice.” But Harris was cold, calculating, and homicidal. “Klebold was hurting inside while Harris wanted to hurt people,” Fuselier says. Harris was not merely a troubled kid, the psychiatrists say, he was a psychopath. In popular usage, almost any crazy killer is a “psychopath.” But in psychiatry, it’s a very specific mental condition that rarely involves killing, or even psychosis. “Psychopaths are not disoriented or out of touch with reality, nor do they experience the delusions, hallucinations, or intense subjective distress that characterize most other mental disorders,” writes Dr. Robert Hare, in Without Conscience, the seminal book on the condition. (Hare is also one of the psychologists consulted by the FBI about Columbine and by Slate for this story.) “Unlike psychotic individuals, psychopaths are rational and aware of what they are doing and why. Their behavior is the result of choice, freely exercised.” Diagnosing Harris as a psychopath represents neither a legal defense, nor a moral excuse. But it illuminates a great deal about the thought process that drove him to mass murder."