Law & Order: Special Victims Unit S03 E04 Rooftop

"Hope in the darkness."

When an HIV-positive male, with a record of assaulting underage girls, is discovered in a sexual clincher with a young woman on a rooftop, the detectives are determined to put him back inside. After a series of rapes and murders of young African-American women cannot be traced to him though, they begin to wonder if they've been looking at the wrong suspect.