Why do FBI agents call the killer an unsub?
The term "Unsub" is short for "Unknown Subject", or a suspect that hasn't yet been identified.
In criminal justice, and unsub is an unknown subject. This person is believed to be the source of criminal activity, and evidence ties a crime or multiple crimes to this one person. The term is often used on the show Criminal Minds to refer to a serial killer who the FBI is learning about but has not yet identified.
FBI weapons FBI now issue the Glock 23 to all Special Agents on graduation. Agents are able to purchase and carry the smaller Glock 27 (subcompact 40 cal.) as a back up. The most commonly used sub-machine gun is the Heckler and Koch MP5/10, the 10mm variant of the famous MP5 However the FBI issues all agents a 12 gauge shotgun and most agents are also issued an M-4 (.223).