investigator

1 one who observes or studies by close examination and systematic inquiry investigators who discovered new evidence that the universe was much older than had been previously estimated Synonyms experimenter, researcher Related Words monitor, observer; empiric, empiricist, fact finder; field-worker; examiner, inspector

2 a person not on the police force who investigates criminal or illicit activity or searches for missing persons the investigator in charge of the case was touted as an expert at tracing stolen art Synonyms dick, gumshoe, hawkshaw, detective, operative, private detective, private eye, private investigator, shamus [slang], sherlock, sleuth, sleuthhoundRelated Words shadow, tail, tracer, tracker; fed, Federal, G-man, narc (or nark) [slang], plainclothesman