(n.) One who instructs by question and answer, especially in religions matters.

Bow Street runner FBI FBI agent Federal G-man MP Secret Service Sherlock Sherlock Holmes T-man asker bailiff beadle beagle bound bailiff captain catchpole catechist chief of police commissioner constable cop copper cross-interrogator cross-questioner deputy deputy sheriff dick examiner eye fed federal flic gendarme government man gumshoe hawkshaw hotel detective house detective house dick inquirer inquiry agent inquisitionist inquisitor inspector interlocutor interpellator interrogator interrogatrix interviewer investigator lictor lieutenant mace-bearer marshal mounted policeman narc officer operative opinion-sampler patrolman peace officer peeper plainclothesman police captain police commissioner police constable police detective police inspector police matron police officer police sergeant policeman policewoman poller pollster portreeve private detective private eye private investigator prober querier querist questioner questionist quizzer reeve revenuer roundsman sampler secret agent sergeant sergeant at arms sheriff sleuth snoop snooper store detective superintendent tec tipstaff tipstaves treasury agent trooper