S12, E15: Tracy Conley is found stabbed to death and buried under piles of garbage in front of an apartment building. The detectives eventually discover that she had spent her last hours with her Little Sister, a 15-year-old girl named Monique (Yaani King) who had discipline problems. It turns out Monique had set up Tracy to be mugged by a drug dealer. The Detectives believe the dealer, Arnold (Haasan Iniko Johnson), killed Tracy. But he claims he only took her purse, and says that a man jumped in to rescue her so he took off. In the meantime, the Detectives are suspicious of one of Tracy's colleagues, Dr. Craig Gerring, who is caught trying to steal Tracy's laptop.