Is ITV crime drama The Pembrokeshire Murders based on a true story?

Well, the answer is very accurate: the three-part miniseries is based on a book by Steve Wilkins and ITV journalist Jonathan Hill – who appear as main characters in the drama – and largely sticks to the true story.

Yes, although some aspects of the story might seem a little far-fetched, none of the major events in the series are added for effect – the only real changes are the names of a few characters, some of whom are actually amalgamations of various real-life people

If you're amazed at the fact all these events really happened, then you're in good company. Star Luke Evans himself has said that he was staggered when he learned about some of the real-life events, explaining to RadioTimes.com and other press: "Literally, when I read the treatment I remember sitting in my trailer and I started Googling it!"

He added: "But when I read the story I realised that there were no fictional embellishments in the story, this is as true to the fact as it possibly can be. And it really is a rollercoaster ride as you watch it, every twist and turn and then this glimmer of hope, it just keeps you on the edge of your seat which is just what you want from drama."

Meanwhile, Evans' co-star Alexandria Riley, who plays DI Ella Richards - an amalgamation of various police officers on Wilkins' team – explained how she remembers watching the case unfold at the time.

"It was completely surreal, it was stranger than fiction, and I just remember the horror and shock in the family home and with friends," she said.

"The fear that something like this could happen so close to home, and just how stranger than fiction this was, it couldn't possibly be real in such an idyllic and beautiful little town. It shocked us all to the very core really, it did play out like a movie."

We've put together everything you need to know about the real-life case below – including a timeline of events and a deeper dive into some of the key aspects of the story.

Timeline of events

December 1985 - Double murder of siblings Richard and Helen Thomas

May 1989 - John Cooper is a contestant on Bullseye

June 1989 - Double murder of Peter and Gwenda Dixon

March 1996 - Milford Haven attack on five children

2005 - Operation Ottawa begins and the double murder investigation is reopened

2008 - John Cooper is released from prison after serving 14 years for robbery and burglary

2011 - John Cooper is sentenced to life imprisonment for the double murders of Richard and Helen Thomas, Peter and Gwenda Dixon and for the Milford Haven attack

We've gone into some more detail about certain aspects of the real-life case below:

Bullseye appearance

Undoubtedly one of the key moments in the programme, and one aspect from the true-life case that stands out as almost stranger than fiction, is the fact that John Cooper appeared as a contestant on the popular darts games show Bullseye shortly before he committed his second double murder.

This might seem like a throwaway piece of trivia, but it actually played a crucial role in helping to convict the killer. At the time when Wilkins learned of Cooper's appearance on the show, he and his team had been desperately looking for pictures of him from the period to compare with an artist's sketch of the main suspect, and they had come up short before they found the Bullseye footage.

What's even more remarkable is that he came across the Bullseye footage by complete coincidence – as depicted in the programme, he was tipped off by the landlord of a pub he was drinking at after his son's football match, after seeing a photo of Cooper as part of the pub's darts team on the wall.

Executive producer Simon Heath explained: "I mean it was a huge breakthrough in the case because though there'd been an artist's impression done for a potential suspect in the second double murder, what John Cooper had cleverly done is destroy all photos of himself from that era.

"So there was no contemporary reference point of Cooper next to the artist's impression, and that was an ongoing problem for Steve, regardless of the forensic evidence that he was starting to carve out.

"And then he discovered almost at random after one of his boy's football matches that the pub he was in was the pub that Cooper had used to play darts at and there was a picture of Cooper on the board. He was the captain of the darts team and the landlord tipped him off that actually he'd been on Bullseye, years before, so with the help of Jonathan Hill who'd been reporting on the case, they tracked down the footage to the ITV archive in Leeds.

"And we, as part of the making of the show, got hold of the same footage – and then we were left with the problem of how could you incorporate it within our fictional depiction of the story so what we actually did was we superimposed through VFX a de-aged version of Keith Allen on to the original footage of Cooper and I think that it's testament to the technical guys, they've done a fantastic job and it's very convincing."

Blood on the shorts

Along with the footage, the other thing that Wilkins and his team relied on to convict Cooper was forensic evidence – and this was something they had to search long and hard for.

In the end, they managed to track down a pair of shorts that Cooper had had altered by his seamstress wife Pat, who had been unaware that she was accidentally preserving a speck of one of her husband's victim's blood – by sealing it within the hem of the shorts.

Writer Nick Stevens said, "It's a great metaphor isn't it that the truth will out. Pat Cooper, who was an accomplished seamstress, had been told by her husband to alter these shorts because they were, in fact, women's shorts and because Cooper had taken them from the belongings of one of the victims after he'd killed her.

"He was obviously self-conscious about the fact that they were women's shorts and they were too long and so he got his wife to alter them not knowing that a speck of one of the victim's blood was hidden and in the process preserved for twenty odd years –so that (forensic scientist) Dr. Angela Gallop and her team could find it, you couldn't make it up!"

The huge developments in forensic science that had been made in the two decades between the murders and the conviction were key to solving the case, and this was something that had really scared Cooper while he was still in prison serving a sentence for burglary.

Indeed, Cooper regularly watched ITV News in prison, and when he found out that the case was reopened and they were searching for new evidence, he immediately took out all the relevant books from the prison library.

As Simon Heath explained: "It completely spooked him, and bear in mind this is an era where there were new forensic technologies coming alive, Dr. Angela Gallop was one of the pioneers there, she'd been involved in the Damilola Taylor case, the Stephen Lawrence case, the Lynette White case and she knew about these technologies but generally the public didn't. And so Cooper wanted to become the world's expert on DNA."

John Cooper's son

A part of the story which is touched on in Wilkins and Hill's book but which is explored in greater detail in the series is John Cooper's relationship with his son Andrew – who he frequently bullied and attempted to implicate in the murders long after the two had broken off contact.

Nick Stevens said: "One of the discoveries I made in the course of reading the book was this detail when the detectives interviewed Cooper, they interviewed him over the course of three days, and whenever he felt under threat he would implicate his son, Andrew.

"In the book, it was very clear that Steve Wilkins was disgusted by this strategy as any parent would be, why would you implicate your son in such terrible crime, and it gave me a real fire to find Andrew and tell his story."

And so Stevens and the rest of the team set out to find Cooper's son, and although it was a challenge to track him down he eventually agreed to come on board.

"It was quite a job to find him in the first instance because he lives very much under the radar," Stevens explained. "Jonathan Hill the ITV journalist was the one who found him and I was quite apprehensive about the first meeting. Here's a TV writer wanting to burrow into the darkest recesses of this man's private life, but he was never anything but totally generous and open and he saw this as an opportunity to set the record straight to tell his side of the story.

"And maybe revenge is too strong a word but he had a score to settle with his absent father and he saw this drama as an opportunity to do precisely that."

Steve Wilkins and his son

The relationship between John Cooper and his son isn't the only father/son relationship explored in the miniseries, we also see several scenes play out between Steve and his son Jack (whose real name was omitted from the programme.)

In the programme, the pair are seen to have a slightly strained relationship due to Steve spending so much time at work and often missing his son's football matches, but by the end of the series it becomes clear that Jack is inspired by his father.

Stevens explained: "In episode three, it ends with Jack telling his dad once the case is over, once there's been a success, that he wants to be a copper – and that is actually exactly what's happened, that's the truth!"

Luke Evans added: "We met the whole family and [Steve's son] is a charming young man and followed in his father's footsteps which says an awful lot about who his father is as a detective and a crime solver but also as a father."

What did the real-life Steve Wilkins and Jonathan Hill have to say about the programme?

Both Steve Wilkins and Jonathan Hill played a huge role in bringing the programme to life, not just because the series is based on their book but also because they acted as consultants and regularly visited the set – which proved an enormous help for the actors.

"He was a huge help," said Evans. "We had Steve and we had Jonathan and they were very, very generous with their time and Steve sat with me and sat with Alex [Riley] and we had long days with him where he would talk us through the interrogation process, he would talk us through the moments when he found this glimmer of hope within this one piece of forensic evidence, the moment when he realised that he had the guy.

"He was extremely generous with not just the technical side but the emotional impact it had on him and on his family, because what really drew me to the storyline is that this wasn't just about finding the killer, it's about this man who had to sacrifice time with his family."

As for Wilkins himself, he said that it felt "quite surreal" that an ITV drama was being made about the case.

"I had been told ITV were interested but then I thought, ‘is this really going to happen’," he said. "Then suddenly it becomes reality, there’s a writer, and it seemed to take on a life of its own. I still can’t really believe that the story is going to be on TV.”

Speaking about being played by Luke Evans, he added, "It’s a privilege to know someone of his ability and his reputation is doing it. I met him with Jonathan in Cardiff before filming started and what a lovely guy, very down to earth.

"I was really impressed with his knowledge of the case and his humility and sensitivity to the investigation and towards the victims, he was highly professional."

Meanwhile, Jonathan Hill explained that he had been wanting a drama to be made about the case for some time, revealing that he "was writing letters to various commissioners" before writer Nick Stevens approached him.

Hill also explained how he was on set during several key moments to advise – including the recreation of the news broadcast that was made for John Cooper, while he also had lots of words of praise for the performances.

Speaking about Keith Allen's turn as John Cooper, he said: "Keith absolutely inhabited Cooper. He is such an interesting actor anyway but the menace he brings while also bringing this charming, grandfather figure at the same time. I think it will go down as one of his great roles."

The Pembrokeshire Murders begins on Monday 11th January at 9pm on ITV. Looking for something else to watch? Check out our TV Guide.