A serial killer is typically defined as an individual who haes killed three or mair fowk ower a period o mair than a month, wi doun time (a "ceulin aff period") atween the murthers, an whose motivation for killin is uisually based on psychological gratification. Some sources disregard the "three or mair" criteria, an define the term as "a series o twa or mair murthers, committit as separate events, uisually, but no aye, bi ane affender actin alane" or, includin the vital characteristics, a minimum o twa murthers. Aften, a sexual element is involvit in the killins, but the FBI states that motives for serial murther include "anger, thrill, financial gain, an attention seekin". The murthers mey hae been attemptit or completit in a similar fashion an the victims mey hae haed something in common, for example, occupation, race, appearance, sex, or age group.
The term an concept o the "serial killer" is commonly attributit tae umwhile FBI Special agent Robert Ressler in the 1970s. Author Ann Rule postulates in her 2004 beuk Kiss Me, Kill Me that the Inglis-leid credit for coinin the term "serial killer" goes tae LAPD detective Pierce Brooks, creator o the ViCAP seestem. Creeminal juistice historian Peter Vronsky, in his beuk Serial Killers: The Method and Madness of Monsters, while arguin that umwhile FBI profiler Robert Ressler micht hae coined the offeecial polis uise o the term "serial homicide" when guest lecturin in 1974 at the British Bramhill Police Academy in Britain, states that the terms "serial murther" an "serial murtherer" appear in 1966 in John Brophy's beuk The Meaning of Murder. Vronsky reports that in Anne Rule's seminal beuk on Ted Bundy, The Stranger Beside Me, published in 1980, the term "serial killer" does no appear an is no yet in popular uise.
- Holmes 2010, p. 39.
- Reavill 2007, p. 228 "With only two confirmed kills, Ed Gein did not technically qualify as a serial killer (the traditional minimum requirement was three), but that did not deny him immediate entry intae the pantheon of folk".
- Holmes 1998b, p. 9 "One of the most famous [geographically stable] serial killers is Wayne Williams. He was convicted of only two killings. However, his probable involvement in more than 30 killings of young black males in Atlanta qualifies him for classification as a geographically stable serial killer".
- Burkhalter Chmelir 2003, p. 1.
- Morton 2005, p. 4, 9.
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- Ressler 1993, p. 29.
- Schechter 2003, p. 5.
- Rule, Ann (2004). Kiss me, kill me and other true cases. Simon & Schuster. Retrieved on 2011-07-16.
- Vronsky, Peter (2004). Serial Killers: The Method and Madness of Monsters. Penguin-Berkley. Retrieved on 2011-09-19.
Freemit airtins 
- Crime Library's Serial Killer page
- Serial Murder: Multi-Disciplinary Perspectives for Investigators Offecial FBI publication