Pembrokeshire Murders: All the clues that led police to catch killer John Cooper
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Killer John Cooper was caught by police after tiny clues were pieced together.
The hunt has been relived in ITV's true crime drama The Pembrokeshire Murders.
Cooper committed his heinous crimes in the Welsh county in the late 1980s, but he remained a free man for years.
On December 22, 1985, he murdered brother and sister Richard and Helen Thomas before burning down their farmhouse.
Four years later, he robbed Peter Dixon of £300 and shot him and his wife Gwenda in the face at point blank range.
And his crimes didn't stop there, he went on to commit a string of other offences, including 30 robberies and violent assault.
Killer John Cooper
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It wasn't until a 2005 cold-case review of the murders that the case was finally cracked thanks to the advances of forensic science.
But what were the vital clues that led to the murderer's capture?
The Bullseye Killer
Cooper carried out his second brutal double killing three weeks after he had appeared on darts-based TV show Bullseye.
He told host Jim Bowen about the area he lived in and how much he loved it, even mentioning the spot where he would later claim the lives of the Dixons.
Footage from his appearance on the game show was used to catch him when it was compared to a suspect sketch created following the 1989 murders.
It was for that reason that he was named The Bullseye Killer.
He appeared on Bullseye weeks before his second double murder
Cooper had ended the lives of siblings Richard and Helen Thomas, aged 58 and 54, by shooting them in their remote Scoveston farmhouse in 1985, before setting it on fire and destroying crucial evidence.
In 1989, he took the lives of holidaymakers Peter and Gwenda Dixon, aged 51 and 52, on the Pembrokeshire coast path, shooting them both in the face.
The married couple were found concealed close to the path on the edge of a 60-metre-high cliff, around six mile from where the Thomas siblings were killed.
Peter had been forced to hand over his bank card and PIN number, and it was used four times to withdraw money after his death.
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A shot of him on the show was compared to this 1989 suspect sketch provided by a witness
A member of the public gave police a description of a man wearing shorts acting suspiciously as he withdrew cash.
And when police officers discovered Cooper had appeared on Bullseye in May 1989, they managed to freeze a frame of him standing in the exact same position as this artist's impression of the wanted kiler.
A tiny clue in the killer's kitchen
For forensic scientist Professor Angela Gallop and her team, a clue found in Cooper's kitchen became a crucial piece of evidence in bringing him to justice.
A pair of shorts that had been left strewn on top of his kitchen units provided police with the evidence they needed.
She told the Mirror how she helped find this "golden nugget" of evidence needed by Det Supt Steve Wilkins, who is portrayed by Luke Evans in the mini-series.
Peter and Gwenda Dixon
She said: "I was initially called in to review DNA samples only.
"My team of scientists trawled through hundreds of crime scene items and did not find anything new."
But after digging deeper, she found the damning evidence in traces of fibre.
She went on: "After 18 months, we had what I would politely describe as a frosty meeting with the police, they were frustrated that we had not found the nugget Steve wanted. I understood why they were so I asked them to expand their remit and let me look at more than DNA. I wanted to explore textile and fabric links as they had in other cases led us to DNA.
Richard and Helen Thomas
"We then started looking at other items relating to Cooper, including a pair of shorts found atop of his kitchen units. Under a microscope and on the lower left leg of the shorts was the tiniest piece of evidence – a blood stain that matched Peter Dixon’s DNA. It was the golden nugget – linking him to the one of the double murders was finally discovered."
Fibres found in the shorts pockets were also found to be similar to those on part of Mr Thomas' socks which were salvaged from the fire-ravaged murder scene.
Cooper's black-painted sawn-off shotgun, which was found discarded in a hedgerow, also provided vital clues.
Professor Gallop says that minuscule paint flakes found in the bottom of the bag it had been stored in were tested, and blood was found.
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Blood was found on the shotgun
"Some appeared to have a reddish cast to them which tested positively as blood," she said.
More scrapings of the black paint were taken from the weapon and blood was found on the surface. DNA testing showed it was Mr Dixon's blood.
What happened to Cooper
When police had enough evidence to convict the killer, he went to trial, where he denied the murders.
He was found guilty and given a whole life jail sentence in 2011.
Now aged 76, he is a diagnosed psychopath.
No clear motive has ever been established for the killings.
Angela, who was awarded the CBE in 2015 for services to forensic science and is played by actress Anastasia Hille in the TV drama, said: "He wasn’t as smart as he seemed to think he was – these days science is always one step ahead of the crooks I have helped bring to justice and that pleases me. He obviously does not know much about forensic science!"