God Told Me To (1976) Larry Cohen

When a sniper shoots people on the streets of New York from the water tank, the religious detective Peter J. Nicholas climbs the stairs to talk to the criminal and learn his motives for the death of 15 persons. He answers "God told me to" and jumps off, committing suicide. There are two other crime sprees in New York, and the killers give the same answer. Soon Nicholas goes to a crime scene where a family man killed his wife and two children and he tells the same to Nicholas. He investigates further and learns that before the wave of killing, each murderer talked to a hippie-like man named Bernard Phillips. Nicholas becomes a whistleblower and leaks the information to the press. Meanwhile he seeks out the mysterious Bernard Phillips and also learns about his own past.