sleuth

a person not on the police force who investigates criminal or illicit activity or searches for missing persons <the popular TV sleuth lives a much more action-packed life than do his real-world counterparts> Synonyms dick, gumshoe, hawkshaw, investigator, operative, private detective, private eye, private investigator, shamus [slang], sherlock, detective, sleuthhoundRelated Words shadow, tail, tracer, tracker; fed, Federal, G-man, narc (or nark) [slang], plainclothesman