S12, E13: Two young women are found murdered in their apartment. A party was in progress across the hall and the police question several possible suspects, but eventually realize their killer is still at large. One of the victims liked to party and was actually scoring heroin for a friend earlier that night, but those leads also turn up empty. The detectives then realize that whoever committed this heinous crime must have had access to the building because no one was "buzzed" in prior to the murders. One of the tenants says he saw a man in a workman's type uniform leaving the building, so the detectives question the super's assistants who have done work in some of the apartments giving them access to keys, but that doesn't pan out. They start to check out local locksmiths in the area, and they find one where all the employees wear the same type uniforms as the super's assistants.