I don't know how do you use the word "agent" in USA. For me this means a man in a suit (FBI, CIA etc.) but I can be wrong, American people know such things better. I'm not sure that it was a government position, it could be a private jail as well.

Actually, that guy Zimmerman, who killed Trayvon Martin, had an attack on a police officer in his list, nevertheless he was a vigilante of a Neighborhood Watch and had a gun.