This exclusive clip from the documentary provides a look at how police found suspect John Cooper on '80s game show Bullseye.
- The answer lay in an unlikely place.
- We were aware that Cooper had been on "Bullseye" from quite an early stage. But what we didn't know was what the significance of his appearance on "Bullseye" could be.
- On "Bullseye."
JONATHAN HILL: It was this legendary game show hosted by Jim Bowen-- hugely popular-- and the contestants had to answer general knowledge questions, and then also play darts to win the prizes. And Steve said, look, any chance you can see if you can find this?
JONATHAN HILL: It was like looking for a needle in a haystack, because they made countless episodes of "Bullseye." They're still running it on channels now.
- Who would you like to be if you weren't you?
- My husband, because he don't work as hard as I do.
JONATHAN HILL: Had to get hold of an archivist who was looking after the shows. They were all stored in a basement in Leeds. And it required a bit of sweet talking, and a bit of arm bending to get him to go through all the episodes and look for a contestant that was from Pembrokeshire.
- Listen, what you want--
- There was no list of the contestants on ITV records. The archivist hunted through videotapes of hundreds of programs.
JONATHAN HILL: I got a call from the archivists who said, I think I found it.
- John and Harvey with 220 pounds, please.
JONATHAN HILL: He said there's a guy here, and he's with a friend, and they're from Pembrokeshire. I can remember thinking, well it was an amazing moment to think we'd found it.
- You've got an unusual hobby, John, haven't you?
- Oh, yes, the scuba diving--
- The scuba diving. And apparently, it's the place to do it down there, isn't it?
- Oh, we've got the coastline, yes.
- Because, yeah, because.
- I get a call from a very excited Jonathan Hill, and they've actually identified the particular program in the recording. And significantly, it is three weeks before the Dixons are murdered.
- We'd like to [INAUDIBLE].
- There it is. I'll keep.
JONATHAN HILL: We just took the artist's impression, and then we took a freeze frame, just like you do at home on a DVD player. You know, you press pause at the most likely moment.
- You get the 220 pounds back. It's-- we know you're a good player. I just.
JONATHAN HILL: And suddenly, those two images came together.
- It was unbelievable. In my 33 years in the police, I've never seen a comparison between an artist's impression and that of a suspect. It was like a tracing.
JONATHAN HILL: There he was on "Bullseye" just a month before he killed the Dixons.
- The Ottawa detectives were ready to charge Cooper with four murders and a rape. But now everything rested with a jury.
- You will judge me after the trial, not before. Judge me after the trial.