examiner

A person who investigates someone or something.

Younger [Customs] examiners, who, perhaps, have not yet acquired the intuition resulting from years of experience, seem partly responsible for the closer examination of incoming luggage. Not only is this closer scrutiny arousing feelings of resentment among passengers, but it is causing serious delays in the departure of boat trains, many of which have been reaching their destinations two or three hours late.

A person who sets an examination.

A person who marks an examination.