James Alan Fox: I started studying mass murder in the early 1980s (along with Northeastern University colleague Jack Levin) to see if there were any common traits and characteristics to the crimes or the perpetrators. There had been a pervasive sense back then that mass murderers were crazed lunatics who suddenly snapped, went berserk, and killed indiscriminately. By studying 42 cases that had occurred in recent years (recent back then, anyway), we found that many common assumption were quite off the mark…

Most mass killers kill people they know, with a clear-cut motive. They typically plan their crimes in advance, often weeks or months in advance. They are calm, deliberate and determined to get justice for what they perceive to be unfair treatment.

The idea that they suddenly snap actually makes little sense. They snap and just so happen to have 2 AK-47’s and 2000 rounds of ammunition around for just such an occasion? Hardly. …

Most of the time, the motive is to get even with those they hold responsible for their misfortunes. Usually people at work or at home, or sometimes a class of people (women, Jews, immigrants, whites, blacks, etc) . . . so the victims are chosen randomly, but not the type of victim, or the place to find them.