"Active killer" or "active shooter" names a type of mass murder marked by rapidity, scale, randomness and suicide. The phenomenon is exemplified by massacres at Columbine High School massacre, the Virginia Tech shooting, the Sandy Hook Elementary School shooting, the 2014 shootings at Parliament Hill, Ottawa, the Umpqua Community College shooting, the 2015 San Bernardino shooting, and many others.
The United States Department of Homeland Security defines the active shooter as "an individual actively engaged in killing or attempting to kill people in a confined and populated area; in most cases, active shooters use firearms(s) [sic] and there is no pattern or method to their selection of victims." Most incidents occur at locations in which the killers find little impediment in pressing their attack. Locations are generally described as soft targets, that is, they carry limited security measures to protect members of the public. In most instances, shooters commit suicide, are shot by police, or surrender when confrontation with responding law enforcement becomes unavoidable. According to New York City Police Department (NYPD) statistics, 46 percent of active shooter incidents are ended by the application of force by police or security, 40 percent end in the shooter's suicide, 14 percent of the time the shooter surrenders and, in less than 1 percent of cases, the violence ends with the attacker fleeing, although it must be noted that the report provides no formal definition of the relevant terms and, as a result, the scope of its statistical findings is somewhat ungrounded.