In 1973, the horrific murders of three teenage girls near the steel town of Port Talbot shook a community. A major manhunt was launched, but for decades the murders remained unsolved. This inside story is the companion documentary to the BBC One drama Steeltown Murders.

With revealing interviews from detectives at the heart of the re-investigation and emotional first-time interviews from friends and family of the girls, we hear how, after nearly 30 years, Wales's first serial killer was finally unmasked.

In July 1973, the body of 16-year-old Sandra Newton was discovered in a culvert in Tonmawr, near Port Talbot. She had been raped and strangled on her way home from a night out.

Two months later, 16-year-olds Geraldine Hughes and Pauline Floyd hitched a ride home after a night out in Swansea. The next morning, they were found in woodland, again raped and strangled. Although they occurred nearby, at the time, the murders of Geraldine and Pauline were treated as separate investigations to the murder of Sandra, and despite thousands of police interviews, all three murders remained unsolved.

Decades later, it would take a major breakthrough in forensic science to enable a small team of seasoned detectives to re-open the case. They discovered the same male DNA profile on the clothes of all three girls, revealing for the first time that one man was responsible for all of the murders. They were now hunting for a serial killer.

But with no match on the National DNA Database, the team had to use a groundbreaking technique, now known as familial DNA, to try and find a relative of the killer and get one step closer to the truth.