The murders of a beloved doctor, his wife and their young daughter leave their Santa Barbara, Calif., community reeling; a manhunt leads to the arrest of a suspect who prosecutors say is a conman.

A stalker sends menacing messages to a young mother before she is murdered. The investigation reveals a sinister setup. In this week's 48 HOURS, correspondent Peter Van Sant reports on how law enforcement unraveled the case, including why a person of interest believes the spirit of the victim gave him "the urge" to buy a sweatshirt that ultimately helped clear his name.