Murder trials often turn on tiny pieces of evidence, barely visible to the human eye.

In the case of Sarah Payne, conclusive proof of Roy Whiting's guilt was established by a single strand of the schoolgirl's hair.

It was discovered on his sweatshirt, providing the police with a tangible link between the abductor and his victim.

Deep down, I always thought it was Roy Whiting

Martyn Underhill Detective Inspector

DNA profiling proved beyond doubt that the hair must have come from Sarah. It is the latest example of how this scientific technique has revolutionised the art of detection.

The jury was told that the chances of it belonging to someone else were a billion to one.

Painstaking

It was by no means the only evidence against the accused man, but it was the most damning.

Van: Scrutinised by forensic scientists

Gathering together that evidence, in order to secure a conviction, took an enormous amount of time and skill.

In all, 1,300 police officers were involved in the search for Sarah and the subsequent hunt for her killer.

During the investigation, the police had to answer and assess 17,000 phone calls from members of the public anxious to help.

The whole operation cost more than �2m.

When a farm worker discovered Sarah's partially buried body, the search for a missing girl turned into a murder hunt.

Prime suspect

From the start, the suspicions of the police were focused on Roy Whiting, a local man and a known paedophile. He had already served a four-year prison sentence for abducting a nine-year-old girl.

And he had a white van.

A compelling case

Strand of Sarah's hair on Whiting's sweatshirt Fibres on girl's shoe linked to the white van Receipt from petrol station near burial site Whiting known as a loner without many friends

But proving that he had abducted Sarah was not easy. Like many others who prey on children, Whiting was a devious man determined to give away nothing.

He had even tried to smarten up his appearance to avoid being identified.

Repeatedly questioned by detectives, he would only say he was at a funfair in Hove at the time of Sarah's disappearance.

It was a lie. A receipt from a petrol station proved that he had been in the area where her body was eventually found.

A team of 20 forensic scientists then began a painstaking search of his flat and his van in an effort to find the forensic evidence that would link him to Sarah.

'We've got a hit'

The discovery of a single blond hair on his sweatshirt seemed to be the proof they were seeking, but they still had to prove it came from Sarah.

Scientists extracted DNA from the root of the hair and matched it to a similar sample taken from a tooth recently lost by the eight-year-old and left underneath her pillow.

Sweatshirt: Single hair discovered

It was a crucial piece of evidence, and a picture of Whiting's guilt began to emerge.

After one of Sarah's shoes was recovered, scientists removed more than 350 tiny fibres from the Velcro fastening.

One by one they were analysed under a microscope. Five of the fibres were connected to Whiting and his van.

It all took time, and Detective Inspector Martyn Underhill recalls the moment when the team knew they had made a breakthrough.

"It was seven months before we got a phone call saying we've got a hit, we've got some good results, and that was a very long seven months," he says.

"It was very frustrating for all of us because although we had to keep an open mind, deep down I always thought, as most of us did, that it was Roy Whiting."

Convincing

In the dock at Lewes Crown Court, Roy Whiting shuffled papers and made notes as a series of prosecution witnesses described how they had painstakingly gathered the evidence.

Roy Whiting was on the register of sexual offenders

He seemed almost unconcerned, resting his head on his hand, and occasionally glancing around the court room.

But he must have known that the case against him was becoming overwhelming.

Prosecuting counsel Timothy Langdale QC told the jury that the evidence added up to "compelling proof" of the accused man's guilt.

The chain of evidence was complete. If Sarah Payne had been in Roy Whiting's van, then he was surely the man who seized her, killed her, and buried her.

And that was enough to convince the jury.