Some of these killers are psychopaths, seemingly from birth. Others appear to have had other severe and intractable problems for most of their lives, many despite families that look relatively ordinary. Then there are the seemingly normal individuals who degenerate rather suddenly (sometimes even becoming schizophrenic) before the rampage begins.
We can use words like “sick” or “evil” to describe these people, and those terms are probably appropriate. But that tells us little about how to predict — and especially how to prevent — their explosive violence. For all but the few who give clear advance warnings of the mayhem they are planning, we have no good way of differentiating the ones who will crack and become rampage killers from the far greater number of similarly disturbed people who lead nonviolent and law-abiding lives, or have only minor brushes with the law, or who end up harming only themselves.
We need to do our best to protect ourselves and others against the mass murderer; that’s where all those discussions about armed guards and concealed carry and gun control (both pro and con) come in. But there are no simple answers to the question of what makes mass murderers tick, as desperately as we might want to find them, as much as we would like to comprehend what may be incomprehensible.