Steeltown Murders true story: How accurate is the BBC One drama?

Two previous investigations, which both took place in the 1970s, had been fruitless, leaving the families of the victims without answers and the community of Neath Port Talbot shaken to its core.

Philip Glenister and Steffan Rhodri lead the cast of Steeltown Murders as DCI Paul Bethell and DC Phil 'Bach' Rees, both of whom played key roles in finally closing this harrowing case.

Steeltown Murders true story: What inspired the BBC drama?

The story of Steeltown Murders dates back to the summer of 1973, when the county of Neath Port Talbot suffered unspeakable tragedy as three local women were found dead.

Sandra Newton was the first to be discovered, having disappeared on a five-mile walk home from her boyfriend's house. Two months later, Geraldine Hughes and Pauline Floyd also never returned from a night out in Swansea.

Initially, the two incidents were regarded as separate; an assumption that wouldn't be corrected until many years later.

The later case did, however, spark a major investigation by South Wales police, who questioned a grand total of 35,000 people in connection to the horrifying crime, but made little progress as information on the suspect was sparse.

The only details they had gained from an eyewitness was that the presumed killer was in his early 30s, had bushy hair and a moustache, and drove a light-coloured Morris 1100 – but this left an enormous number of potential culprits.

Ultimately, the investigation was a failure, with not one person arrested on suspicion of the murders.

But in the early 2000s, South Wales Police re-opened the cold case in light of advances in DNA technology, which quickly brought new information to light: Sandra's killer was the same person responsible for Geraldine and Pauline's deaths.

"This was an absolute bombshell because this meant there was a serial killer operating in south Wales in 1973 killing young girls," forensic scientist Dr Colin Dark told BBC News.

How DNA evidence identified the killer

Unfortunately, the DNA found on all three of the girls' clothes was not logged on the national database, meaning there was still no easy answer as to the identity of the so-called "Saturday Night Strangler".

However, investigators wondered if they would be able to identify a child or relative of the offender using the sample that they had – a technique now known as familial DNA, which had never been attempted before.

It required trawling through "several thousand DNA profiles from men in the south Wales area", recalled Dr Dark, which gave them 100 individuals that half-matched the sample, suggesting they could be a child of the murderer.

Meanwhile, detectives working on the case had identified 500 of their own suspects based on appearance, car ownership and previous convictions, with the surname Kappen proving noteworthy for featuring on both lists.

Car thief Paul Kappen had half-matched with the DNA sample, but was only seven years old when the murders took place, which brought authorities to his father, Joseph.

Described as a "thug" by DCI Paul Bethell, who led the case known as Operation Magnum, Joseph Kappen had briefly been considered a suspect back in 1973, but was cleared by an alibi from his then-wife and the claim his car was broken down.

Joseph was long gone by the time police were back on his trail – having died of lung cancer in 1990 – but DNA samples from his ex-wife and daughter upped the probability of his involvement in the murders.

Still, it wasn't the absolute certainty that the detectives wanted and the bereaved families needed, so then-Home Secretary David Blunkett approved the unprecedented decision to exhume Kappen's body.

The complicated process began on a stormy night in May 2002, with Dr Dark remembering a clap of thunder sounding at the very moment the coffin was unearthed: "It was the feeling that evil had been identified, it sent shivers down my spine."

Forensic DNA examination of Kappen's remains proved without doubt that he was the murderer of all three women.

Steffan Rhodri, who plays DC Phil 'Bach' Rees in Steeltown Murders, told RadioTimes.com and other press that the case is a testament to the unsung, but instrumental, work that goes into crime-solving.

He said: "The story, crucially, is about the diligence of the police work, rather than the heroics. I mean, it becomes heroic because of the diligence, if you like, but it's not swashbuckling police work of swooping in and glamorous cops saving the day.

"It's about just quite boring, diligent work, that is sitting there poring through lots and lots of detail. I think that very much represents how crimes have to be solved, rather than in a swashbuckling way [or] in a kind of filmic, television kind of way."

How accurate is Steeltown Murders?

The team behind Steeltown Murders told RadioTimes.com and other press that they carried out "meticulous" research into the case in order to bring it to the screen accurately.

"Core to it all was the research that we did," said producer Hannah Thomas. "We worked with the actual police who were on the case – Paul Bethell and Phil Rees – who were there in the 70s, and then also there in the 00s, when Operation Magnum started.

"So they were just a brilliant source of information and guidance for us. And because we're a Wales-based company telling a Welsh story, there's a proximity to the events that was really important for us to take really seriously."

She added: "We were filming where the murders took place, so it isn't at arm's length. It was really, really close to home. So we were very, very cautious and just meticulous in our research and trying to – at every stage – do justice to the three girls who lost their lives.

"We met [with] the families, we were very aware of the reality of what had happened and what they've gone through. So that basically was something really balanced at every stage… that drive to tell a really compelling story, whilst being really mindful of people's grief and that it actually happened."

Screenwriter Ed Whitmore went on to say that his scripts make very few alterations to the true story, besides two tweaks necessary to compress the decades-long case into just four hours of television.

"I think the most common alterations you make to reality are shrinking cast and shrinking time a little bit," he began. "Sometimes things that maybe took place over nine months, you reduce to six months – those kinds of changes.

"The police is a huge, hierarchical structure and there are more players in the story than you could ever capture and you could ever realistically fit into a drama."

He added: "But really, that aside, we changed very little; it was more about what do we leave out? Because the story obviously took place over almost 30 years, so that was really the hardest thing. Where do you put your focus?"

Steeltown Murders premieres tonight, Monday 15th May, at 9pm on BBC One and iPlayer. Check out more of our Drama coverage or visit our TV Guide and Streaming Guide to find out what's on.

Try Radio Times magazine today and get 12 issues for only £1 with delivery to your home – subscribe now. For more from the biggest stars in TV, listen to The Radio Times Podcast.