In the early hours of Sunday, September 17, 1973, the bodies of Pauline Floyd and Geraldine Hughes were discovered in woodland in south Wales. The 16-year-old friends, who worked together in a factory, had gone missing as they hitched a lift home from a night out at the the Top Rank nightclub in Swansea.
They had been raped and strangled before being dumped at the remote rural location. Their deaths sparked a huge manhunt and left a community terrified the killer might strike again.
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It would soon become clear that the same killer had struck two months earlier in a very similar attack. Sandra Newton, also 16, had been found murdered and her body dumped near a disused colliery.
The teen had also been hitchiking and was raped and choked to death with her own skirt before being left in a culvert under a road. All three girls had been lured into a car on a Saturday evening, leading the killer to be dubbed the 'Saturday Night Strangler'.
But it would take nearly three decades of painstaking police work for the murderer to be revealed. And now, the true story of how the killer was eventually discovered has been turned into a major BBC drama, Steeltown Murders, starring Keith Allen and Philip Glenister.
Set in both 1973 and the early 2000s, the four-part series tells how, in the first case of its kind, the mystery was solved using pioneering DNA evidence. So what was the real story of the Steeltown Murders and how was the identity of Wales' first serial killer discovered?
As the murder probe was launched more than 150 police officers chased hundreds of leads and questioned around 35,000 people who fitted a loose description of the man last seen with Pauline and Geraldine. With no mobile phones, no internet and no computers, the investigation soon became swamped in a sea of paperwork as officers struggled to keep tabs on thousands of leads.
The two girls had been seen getting a lift home in a white Morris 1100, a popular car at the time, so more than 10,000 drivers of that model were visited and questioned. Port Talbot steelworks alone employed 13,000 men and all were viewed as possible suspects.
Construction of the M4 was also underway, meaning hundreds of itinerant workers needed to be considered. The murders instilled fear in young women across the community, with posters warning against hitchhiking put up in shop windows.
Police suspected that the same man was responsible for the three murders, however, Sandra's boyfriend was named a prime suspect for her death. He maintained his innocence throughout and was never charged - and later had his name cleared amid breakthrough evidence.
But, despite the amount of resources being thrown at the investigation, it threw up no new leads and eventually it was quietly run down, with boxes upon boxes of evidence and admin shelved. Dr Colin Dark, of Chepstow-based Forensic Science Services, who came to the case in 1990, told WalesOnline: "Much of it went into storage at Sandfields police station in Port Talbot where, because of the damp conditions, it turned to mush.
"It got very mouldy and mice had also nibbled away many index cards. Luckily I anticipated the sort of developments that might happen in DNA research and asked for the girls' underwear to be stored at our labs in Chepstow. The key to cold case work is having material left to work with, you see."
Dr Dark's foresight would eventually crack the case. In 1998, a scientific breakthrough gave the investigation new impetus.
The arrival of an ultra-sensitive testing system meant that the killer's genetic fingerprint, previously mixed up with his victims', could be isolated from the ageing samples available. There were semen stains on Geraldine and Pauline's clothing that matched the same man, but he wasn't on the new DNA database.
A year into the newly established Operation Magnum inquiry, it was then discovered DNA found on Sandra's underwear matched the same man, showing he was responsible for all three murders. But as there was no information on their database, scientists had to get creative.
They had a printout of several thousand DNA profiles to see if there were any children of the offender in the database.
"This was a ground breaking technique, the first time it's ever been done in the UK and possibly the world - and from there, the new investigative tool now known as familial DNA was developed," Dr Dark, whose team was continually checking the sample with new profiles on the ever-growing DNA database, told the BBC.
They came up with a shortlist of 500 men, from which one man, Paul Kappen, stood out. But as he was just seven-years-old at the time of the crimes detectives knew he wasn't the killer. However his dad, Joseph Kappen, known to some on the force as a habitual petty criminal with a violent temper, fitted the description.
Joseph Kappen also drove a Morris 1100 and had been questioned at the time but had an alibi from his wife and claimed the car had broken down on the night of the murders.
But, with his son's DNA providing a link, he became prime suspect. However when police went to take a swab from Joseph Kappen, a nightclub bouncer and part-time bus driver they found he had died 11 years earlier from lung cancer aged 48.
Instead scientists swabbed his ex-wife and daughter, which made up two-thirds of the profile. On Christmas Eve 2001, two years after the cold case was reopened, detectives applied to Home Secretary David Blunkett to exhume Joseph Kappen's body.
DNA taken from the body's femur and teeth proved a full match. The police had finally got their man.
Steeltown Murders continues at 9pm on Monday on BBC One.
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