DNA evidence has already provided a spectacular breakthrough in one long-standing unsolved murder case and is a cornerstone of a current inquiry.

The deaths of Pauline Floyd and Geraldine Hughes almost 30 years ago became known as the Babes In The Wood case.

Joe Kappen's DNA matched the girls' killer

Scientific tests on the body of a man suspected of the serial killings of young girls and women in the early 1970s have shown his genetic profile matches that of the girls' killer.

And mass DNA screening is underway in the reopened investigation into the Cardiff prostitute Lynette White in 1988.

The bodies of Pauline Floyd and Geraldine Hughes were found dumped in woods in Llandarcy, near Swansea, in September 1973. The 16-year-olds had been raped and strangled.

South Wales Police had long suspected a former bus driver and nightclub doorman, Joe Kappen, who died of cancer 12 years ago.

The killings were thought to be linked to that of Sandra Newton whose body had been discovered at Briton Ferry three months earlier.

Geraldine Hughes was raped and strangled

In a dramatic development in June this year, the force revealed samples from Mr Kappen's exhumed body matched those from the Llandarcy murder scene.

Detectives said updated genetic testing techniques confirmed the former nighclub doorman, who lived in Port Talbot, was the rapist and killer who struck in 1973.

Mr Kappen died in 1990 aged 49.

But his family do not accept the claim that their loved one was the "Saturday Night Strangler" and have asked for independent DNA tests on the samples removed from the grave at Goytre Cemetery in Port Talbot.

Even so, South Wales Police have passed the genetic test results on to all the other forces in the UK in a bid to clear-up other unsolved murders.

Sandra Newton was killed first

Humberside Police have revealed they are re-examining the disappearance of nine-year-old Christine Markham.

It is understood Mr Kappen lived in lodgings in the Humberside area soon after Christine's disappearance in May 1973.

DNA testing is also a major hope in another of South Wales Police's unsolved murder cases.

Prostitute Lynette White, 21, was murdered on Valentines Day 1988 in her flat in the Butetown area of Cardiff.

Three men were jailed for life for killing her, but their convictions were quashed on appeal.

Screams

Since then there have been repeated claims that forensic evidence which pointed to two other suspects was not fully investigated.

Detectives have conducted a mass screening of 5,000 people in an attempt to identify who killed he and senior officers have said an important breakthrough has been made using new forensic techniques.

They have been able to recreate the screams heard on the night to see if they could be heard in certain areas around the murder scene.

All five men originally charged with her killing have been told their DNA does not match that of the killer.

A South Wales Police spokesman said DNA testing has proved to a valuable tool in the police's work to land convictions based on the evidence available from crime scenes.

He said: "It allows you to pinpoint someone's profile down to a billion-to-one in some cases.

"It obviously depends on a blanket search."