S12E11 — Mirror Image

The fourth victim of the Mt. Thomas killer has been found in an alleyway near Bill Lapscott's house, using what looks to have been a brick from his yard to knock her out. Confusing the detectives is the fact that a different weapon was used in what seems almost to be a different M.O. The only thing tying her to the other victims is the crucifix, and her history of sexual abuse, leading Garth to suspect there is a copycat killer at work. Amy's theory that Jeff Watts is the killer is proven wrong, since he was under surveillance, but Garth suspects it was Bill. They find him, still at the office, having showered. But there is no evidence to link him to the crimes, since his clothes have no blood on them. Day Six. Searching Ngaire's house, Garth finds a love letter from her to Bill. He claims that he looked after her one night when she was suicidal and she developed a crush on him, which he did not reciprocate. Recognising Garth's own issues, Bill tells him to go to therapy and Garth gets