Four or more murders occurring during a particular event with no cooling-off period between the murders. According to the FBI, A mass murder typically occurs in a single location in which a number of victims are killed by an individual or more. Mass murderers are different from spree killers, who kill at two or more locations with almost no time break between murders and are not defined by the number of victims, and serial killers, who may kill large numbers of people over long periods of time.
