A serial killer is someone who murders several people over a longer period of time, sometimes over a number of years. The victims do not usually know each other, and they do not know the killer. They are connected by the desires of a man they do not even know. The serial killer usually has at least 3 victims. The murders are often very brutal, involving some kind of ritual that has specific meaning only for the offender.
Sexual violence is usually a factor, whether it be before or after death.
Some killers can only get sexual satisfaction through the pain of their victim. Other problems arise in developing a definition for serial killers. For example, would a hit man be a serial killer - they often have numerous victims, but they kill for money. In 1978, the FBI set up a Behavioural Science Service Unit in Quantico, Virginia. At this centre, serial killers are studied, and profiles are compiled on suspects.