Officer Sal D'Angelo is a vice cop and the partner of Peter Ridley. He was on the scene of Tracy Henderson's murder, assumed she was a prostitute, and always aggravated the detectives from a disgust over sex workers and over SVU newer, more compassionate approach.
D'Angelo was suspected of Tracy's murder and other murders in the area since he knew all the murdered women and it was his district. It was revealed, however, Ridley was responsible, except for killing Tracy, who was murdered by Dennis Caufield. (SVU: "Hysteria")