K-Pax - Brewer Gene

When a man who claims to be from outer space is brought into Manhattan Institute, the mental ward seems to be just the place for him. Calling himself 'prot', he says that he is an inhabitant of the planet K-PAX. Setting a departure date - August 17th at 3.31am - on which he plans to return home on a beam of light. Is he really extraterrestrial?