On September 6, 1988, a wealthy couple, Seymour and Arlene Tankleff, were brutally attacked and killed in their home on Long Island, New York. The main suspect was their 17-year-old son, Marty, who was the sole survivor in the house. Detective James McCready was convinced Marty was to blame and prepared a written statement for him to admit he killed his parents. But the physical evidence at the crime scene didn't match the murder weapons described in Marty's so-called confession. Erin Moriarty and retired 48 Hours producer Gail Zimmerman go behind the scenes on a case that spanned nearly two decades and was one of the first wrongful conviction stories they worked on.