By Sangita Myska
Had it not been for one single discovery the high profile murders of Damilola Taylor, Peter Falconio and the school girls Holly Wells and Jessica Chapman would have remained unsolved.
Crucial to each case was DNA evidence.
Sir Alec Jeffreys had taken science by storm with his DNA discovery
Now a key forensic tool, used in crimes from car theft to burglary, sexual assaults to murder, DNA profiling was first used in a criminal investigation 20 years ago in Leicestershire.
In 1986, schoolgirl Dawn Ashworth, was brutally raped and murdered in the village of Enderby.
Her death been preceded by that of Linda Mann in a neighbouring village three years earlier.
A local youth, Richard Buckland, had made admissions about Dawn's killing but with no corroborative evidence, the police couldn't prove he was the murderer.
Desperate for help, they approached the geneticist Sir Alec Jeffreys. Working out of Leicester University, he had recently taken the scientific world by storm.
In the mid-80s Sir Alec had discovered that every person has a so-called DNA "fingerprint" that's unique to them.
It was a chemical code held in every single cell of the human body. Technology developed in his lab allowed him to produce genetic profiles of individuals.
The police hoped this system would help prove their chief suspect Mr Buckland guilty.
Using semen left on the girls' bodies Sir Alec ran a test against blood samples taken from Mr Buckland.
The tests delivered surprising results. They proved that both girls had been killed by the same man - but that that man could not be Richard Buckland.
"It was an incredible moment" says Sir Alec. "We couldn't believe what we were seeing.
"As a man with a young family, living in the local area, I was as keen as everyone else that our discovery should catch the killer. I knew the technology couldn't be wrong. We'd tested and retested our findings."
In a surprise twist, Richard Buckland had just become the first person to be exonerated using DNA profiling.
For the Leicestershire force - it was back to square one. The police realised that to catch their killer they'd have to cast their net far wider.
They decided to undertake the world's first DNA screening programme. Five thousand men gave blood and saliva samples. It was a test that was to change forensic science forever.
Now retired, Ch Supt David Baker headed the murder inquiry at the time.
Having overcome his initial scepticism of profiling he realised that it would be key to finding their killer.
It was he who single handedly persuaded the Home Office to employ the Forensic Science Service to carry out the screening.
"It was a nerve-wracking time," he said. "But the community was behind us. We knew that if the killer was among these men, he'd either turn up or try to avoid us. It turned out, it was the latter."
Within a year, despite an attempt to evade screening Colin Pitchfork, a local baker, was convicted of both murders and sentenced to life imprisonment.
Faced with irrefutable DNA evidence that proved he was the killer, he confessed.
Looking back, Sir Alec says he's astonished at what his discovery has achieved.
"I think people forget that it's not just about proving guilt but about proving innocence," he said.
"The fact is if someone had told me back then, that 20 years hence DNA profiling would be the main forensic tool around the world, that Britain would have a DNA database with nearly 4m profiles on it, that it would be the way to prove paternity, I'd have said it was science fiction."