active shooter

According to the FBI, an individual actively engaged in killing or attempting to kill people with a firearm.

An individual with a weapon is not an active shooter if they have not pulled the trigger.

Until a shot or shots have been fired, think suspect, man with a gun, woman who may have a gun.

The designation exists to alert law enforcement to “an aspect of the crime [that] may affect the protocols used in responding to and reacting at the scene of the incident.”

See also: mass murdermass killing

Note there is no hyphen.