Cruising

Cruising is a movie starring Al Pacino, Paul Sorvino, and Karen Allen. A police detective goes undercover in the underground S&M gay subculture of New York City to catch a serial killer who is preying on gay men.
When New York is caught in the grip of a sadistic serial killer who preys on patrons of the city's underground bars, young rookie Steve Burns infiltrates the S&M subculture to try and lure him out of the shadows.