S3·E17 Avenging Angel

A woman is brutally murdered in her daughter's room at a shelter for battered woman. Her daughter, Julie, is a traumatized eyewitness to the slaying and identifies her father as the killer. Despite her account, Nick and Tracy are unable to find enough evidence to hold or indict him. As they search for the truth, an "avenging angel" decided to take justice into her own hands.