Law & Order: Criminal Intent: Season 4, Episode 18

4 - 18: The Good Child

The slaying of a couple in the Witness Protection Program involves Detectives Goren and Eames as they suspect someone tipped off the murderous clan that seeks vengeance for their testimony -- but the cops discover the victims' surviving daughter and her relationship with her birth father is the missing link. Their investigation reveals that the biological father has a jealous wife and a longtime secret girlfriend -- all of whom have hidden agendas and evil intent.