Maniac Cop (1988) on Netflix

Innocent people are being brutally murdered on the streets of New York City by a uniformed police officer. As the death toll rises and City Hall attempts a cover-up, Frank McCrae heads the investigation. A young cop, Jack Forrest, finds himself under arrest as the chief suspect, having been the victim of a set-up by the real killer and a mysterious woman phone-caller. Forrest, his girlfriend Theresa, and McCrae set out to solve the puzzle before the Maniac Cop can strike again.