Police and family members have long speculated that whoever killed Mary Petry and Bill Sproat may have known them. There were no signs of forced entry into the apartment, and the brutal nature of the killings indicates an emotional component. But Mary and Bill had no apparent enemies. An unexpected tip came in the mid-2000s, saying a religious figure in Mary's life wanted to punish her for considering pre-marital sex – a theory that Mary’s sister finds bizarre. Several retired police officers share their perspectives on the case, including submitting DNA evidence for matching in a state database.