Bad Seed

S3 E2: Tony Hill works with the police to solve the murder of the Johnsons, who were butchered in their flat. When a second victim, Sarah Maynard, is similarly killed they realize they have a serial killer on their hands. William MacAdam, a one-time killer is now one of Tony's students and these new murders are very similar to the ones he committed 30 years ago. He was released from prison as he was considered rehabilitated and has lost the use of both hands due to severe arthritis. Tony is convinced that MacAdam is their man, but he is quite shrewd and it will be very difficult to get the evidence required.