serial killer

A serial killer is a person who murders three or more people, usually due to abnormal psychological gratification, with the murders taking place over more than a month and including a significant break (a "cooling off period") between them. Some sources, such as the FBI, disregard the "three or more" criterion and define serial killing as "a series of two or more murders, committed as separate events, usually, but not always, by one offender acting alone".