Blind Vision (1992)

William, a lonely mail-room employee, is obsessed with Leanne, a beautiful secretary in his office, who also just happens to live in the apartment opposite his. At home he spies on her with a telephoto-lens camera, and one night he sees her having sex with another co-worker from the office, Gregg. Shortly afterwards Gregg is murdered, and Leanne begins to suspect that William might have done it.