The Pembrokeshire Murders is set to premiere on Monday on ITV - but how much do you know about the terrifying true story behind the Luke Evans drama? Get all the information about the stranger-than-fiction tale here...
The police investigation into two double-murders
The story follows the reopened police investigation in 2005 into two double murder cold cases from the 1980s that took place in Pembrokeshire, South Wales. Siblings Richard and Helen Thomas were discovered dead in their home at Scoveston Park, while four years later, married couple Peter and Gwenda Dixon went missing during a walk and were later found dead on a coastal path.
WATCH: Luke Evans stars in the ITV thriller
At the time, an artist's impression by eyewitnesses showed the suspect to have a shoulder-length mullet, but remained unsolved until it was reopened 20 years later with new technology in place to track down the perpetrator.
John Cooper was the prime suspect
During the reopened investigation, the police narrowed down convict John Cooper as their main suspect and manage to get hold of a taping of his time taking part in the game show Bullseye, which saw him sporting the same mullet as the man in the artist's impression. Alongside the DNA evidence, it confirmed suspicions that John was the culprit.
Did John Cooper confess to the crime?
According to the show's writer, Nick Stevens, Cooper initially tried to pin the blame on his son, Adrian. Nick explained to ITV: "Whenever Cooper felt under threat his knee-jerk reaction was to implicate his son, Adrian. Time and again, he implied that Adrian was the culprit. The actual four-time murderer... it fired me with a determination to give Adrian Cooper a voice in the drama."
He is played by Keith Allen on the show
Where is John Cooper now?
Cooper, 76, was released in prison after an 11-year imprisonment for burglary and robbery to be arrested once again in 2011 for the murders of Richard and Helen Thomas and Peter and Gwenda Dixon, as well as the sexual assaults of two teenage girls in 1995. He now serving a life prison sentence at an undisclosed prison.
At the time of his sentencing, Justice John Griffith Williams said that he was "a very dangerous man, highly predatory who, but for advances in forensic science, may well have continued to evade capture... The murders were of such evil wickedness that the mandatory sentence of life will mean just that. You are a very dangerous man, a significant risk of serious harm".
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