matthews concluded that the lead detective on the walsh case, a man named jack hoffman, had become convinced, despite come peopling evidence, that this man didn't do it. so he confesses to this crime repeatedly, knows things about the crime that only the police knew, yet the legal investigator, detective hoffman, doesn't believe him. why not? >> ego and tunnel vision. the tunnel vision is, you come up with your own hypothesis as to what took place and you work that case to validate your own hi hypothesis. >> reporter: matthews made a major discovery. a roll of film from the crime scene of tulle's car, film that the original detectives never bothered to have dropped. the film contain what matthews considered to be a monumental revolution. on the rear floor bard of the car, where tulle admitted to tossing adam's severed head, the outline of a face with a darkened eye sockets and open mouth. >> you see his image. it's as clear as the, you know, shroud of turin. >> to me, it was the one thing that a mother knows, is that this is their child. this picture is their child. >> reporter: in 2008, bas