Repeat killers

A serial killer is typically a person who murders three or more people, usually in service of abnormal psychological gratification, with the murders taking place over more than a month and including a significant period of time between them. Different authorities apply different criteria when designating serial killers; while most set a threshold of three murders, others extend it to four or lessen it to two. The Federal Bureau of Investigation (FBI), for example, defines serial killing as "a series of two or more murders, committed as separate events, usually, but not always, by one offender acting alone".

Although psychological gratification is the usual motive for serial killing, and most serial killings involve sexual contact with the victim, the FBI states that the motives of serial killers can include anger, thrill-seeking, financial gain, and attention seeking. The murders may be attempted or completed in a similar fashion. The victims may have something in common, for example, demographic profile, appearance, gender or race. A serial killer is neither a mass murderer, nor a spree killer.

The English term and concept of serial killer are commonly attributed to former FBI Special agent Robert Ressler who used the term serial homicide in 1974 in a lecture at Bramshill Police Academy in Britain. Author Ann Rule postulates in her book, Kiss Me, Kill Me (2004), that the English-language credit for coining the term goes to LAPD detective Pierce Brooks, who created the Violent Criminal Apprehension Program (ViCAP) system in 1985.

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