Mass murder (sometimes interchangeable with "mass destruction") is the act of murdering a number of people, typically simultaneously or over a relatively short period of time and in close geographic proximity. The FBI defines mass murder as murdering four or more persons during an event with no "cooling-off period" between the murders. A mass murder typically occurs in a single location where one or more people kill several others. Many acts of mass murder end with the perpetrator(s) dying by suicide or suicide by cop.