Criteria

To be classified as a serial killer, a person must have killed more than three people over a period of a month. Not to be confused with spree killers, though the two are similar with differences in their "cool down" period. The cool down period refers to the time between kills, which eventually shortens as these killers start to murder people to experience a pleasurable high. There are other things to look for, such as the Macdonald Triad (animal cruelty, setting fires, bedwetting) and what type of serial killer they are. Thrill seekers, mission oriented, visionaries, and finally power and control killers make up four categories for why they kill.