S11 E11: When seventeen year-old Andrea McWilliams is found strangled and beaten to death in an alley, her ex-boyfriend leads the cops to a website that McWilliams used to meet up with random men. Detective Olivia Benson (Mariska Hargitay) decides to create a user account for the site and finds womanizer Peter Butler (guest star Brian Geraghty), the man who met up with McWilliams. The case is closed when a different suspect is proven guilty of her murder, and a new one opens when McWilliams' rape kit tests positive for HIV. Not only is HIV spreading as a result of countless attacks, but now the detectives must also catch a rapist on the loose. Also starring: Christopher Meloni (Detective Elliot Stabler), Dann Florek (Captain Donald Cragen), Richard Belzer (Detective John Munch), Ice-T (Detective Odafin Tutuola), Stephanie March (ADA Alexandra Cabot), B.D. Wong (Dr. George Huang), Tamara Tunie (M.E. Warner) and guest star Jack Larson (Peter Butler).