Law & Order: Criminal Intent (2001)

Season 4: Episode 18

After Dennis and Camille Burnett are found dead in their home, the only survivor is their twenty-year-old daughter, Rachel. Goren and Eames initially suspect that someone connected with the Marinko family had the Burnetts killed, since they were in witness relocation, but the detectives soon realise that the connection isn't the parents, it's the daughter. Suspicion then turns to the daughter's biological parents and her birth father's very jealous wife.