Obsession

S2 E3: When an alleged stalker breaks into a famous pop singer's house, Don and his team are brought in to lead the investigation. Using the fan letters she received as evidence, Don turns to Charlie, who uses Forensic Information System for Handwriting and discovers that there are two senders, one of them a copycat. The agents are thrown another curve when a celebrity photographer taking photos of the pop princess' house is murdered, and they learn that the pop princess may not be so innocent.