Definition of unknown subject of an investigation in English English dictionary
Unsub is a law-enforcement slang acronym for "Unknown Subject Of An Investigation". The term was frequently used with this meaning on the CBS drama Criminal Minds, a crime procedural dealing with an elite team of FBI profilers. A less common replacement for "perp" or "suspect". It may also have come from "unsubstantiated," referring to charges against an individual that have not been proven