Serial Killer

A serial killer is traditionally defined as an individual who has killed three or more people over a period of more than a month, with down time (a "cooling off period") between the murders, and whose motivation for killing is usually based on psychological gratification. Some sources, such as the FBI, disregard the "three or more" criteria, and define the term as "a series of two or more murders, committed as separate events, usually, but not always, by one offender acting alone" or, including the vital characteristics, a minimum of two murders.