Luckily, serial killers are quite rare but they tend to get intensive media coverage when they come to public attention. Unfortunately, this may serve to encourage the behavior. It is hard to determine exactly when a murderer becomes a serial killer. One definition includes any one who commits at least four murders. Serial killers tend to act alone or with an accomplice and they generally kill strangers. Importantly, they kill for their own psychological gratification, rather than for money, power, or political purposes. Most derive sexual pleasure from their crimes, which tend to be ritualistic 6 and sadistic.

Forensic psychologists say that serial killers are motivated by the sense of absolute power over their victims, and that they spend a good deal of time fantasizing about and planning their crimes. Not surprisingly, most serial killers are profoundly emotionally disturbed and many report traumatic and painful childhoods. In one small study from 1988, 69 percent reported a history of alcoholism in their family and 74 percent reported psychological abuse in childhood. Nonetheless, serial killers do not tend to be very impulsive. In fact, the most successful serial killers can effectively plan their crimes and escape capture for decades.