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 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) defines serial killing as “a series of two or more murders, committed as separate events, usually, but not always, by one offender acting alone”. (Wikipedia)
