TV appearance helped capture of one of Britain's most elusive serial killers

A murder investigation can turn in the most unlikely of places.

And nowhere was that more evident than the television appearance that helped police put away one of the UK's most notorious serial killers.

Back in 1989, John Cooper appeared as a contestant on the hit gameshow Bullseye.

The premise of the series saw amateur darts players compete for cash and prizes, from caravans to speedboats.

But while Cooper left the series empty-handed, the episode would eventually become a key piece of evidence for the murder of Peter and Gwenda Dixon.

The pair of holidaymakers were robbed at gunpoint and killed near a coastal cliff edge in Pembrokeshire just three weeks after the episode aired.

ITV

As well as being a prolific burglar in the Welsh village of Milford Haven, Cooper had also murdered two people four years before appearing on Bullseye, it was later found.

And while police believed he may have had something to do with the deaths of Mr and Mrs Dixon, it wasn't until 2008 that they were able to link him to the crime.

Retired chief superintendent Steve Wilkins was contacted by ITV presenter Jonathan Hill, who had uncovered footage from Cooper's appearance on the gameshow.

And the pair were stunned by what they saw.

The first shocking moment was when Cooper revealed that he had a fairly 'unusual' hobby, which police would later use to put him at the scene of the murders of Mr and Mrs Dixon.

When asked what it was, he said: "Oh yes, the scuba diving … on the coastline.

ITV/Challenge

"We’ve got deep water where you can swim over mountains and all sorts of things."

Recalling the moment he saw the episode, Wilkins said: “You could hardly make it up. There was Cooper, just a month before the killings, revealing on national television knowledge of the area where the Dixons would be murdered.”

But it wasn't just what he said that aroused suspicion, his physical appearance also matched a police sketch of the murderer.

And Wilkins was able to show that Cooper was the man they were looking for.

“We had the prime suspect on tape just a month before the Dixons were murdered," Wilkins explained. "His physique, haircut and features could all be scrutinised.”

Pausing the footage, Wilkins and Hill were able to compare the artist's depiction and Cooper side by side, with the pair adopting a similar pose.

“Cooper had long, bushy collar length hair just like the artist’s impression,” Wilkins said.

ITV

“Given that Cooper’s hair is likely to have been brushed into shape by a makeup artist before the TV show, it matched closely.

"His features too bore a close resemblance, particularly the nose and chin.”

He went on: “For the first time we could see Cooper as he would have looked at the time of the Dixons’ murder.

“In my 30 years service I had seen many artist’s impressions and photo-fit efforts, but I had never seen as close a match as this.”

As well as the videotape, small traces of blood found on clothing from Cooper’s home were also vital in bringing him to justice.

And in 2011, Cooper was sentenced to life imprisonment.