The abduction and murder of eight-year-old Sarah Payne in July 2000, while on a family day out to the Sussex seaside, shocked the nation.

Now for the first time police and forensic scientists give the inside story of how they investigated her disappearance and how car mechanic Roy Whiting - who had a previous conviction for an indecent assault on an eight-year-old girl - was arrested and found guilty of her murder.

Narrated by Mark Austin, Real Crime: The Fight for Sarah’s Law retells the story of Sarah’s disappearance; examines the police investigation into finding her and looks at the campaign waged by Sarah’s mother, Sara Payne, for a change in the law – to give every parent the right to know if a convicted paedophile is living in their area.

For the last eight years Sara has fought tirelessly for Sarah’s Law, so that parents, schools and carers will know where convicted paedophiles are – and now the government has agreed a trial version of the law will be introduced in four areas of England.

Sara tells the programme: “Sarah’s Law is basically about predatory paedophiles. It’s about people like Roy Whiting. If a predator lives in your community you should be able to go and ask and somebody should tell you that he is there.”

Sara speaks frankly to Real Crime: The Fight for Sarah’s Law of how she and her family dealt with the disappearance of her daughter and the feelings of guilt she still suffers for leaving her children on the beach that day.

She says: “As a parent you make decisions no matter what and you have to live with those decisions, unfortunately. But that is what I live with.”

Sara talks about the moment she realised Sarah was missing and the programme features the recording of the 999 call she made.

Senior officers tell the programme about their investigation into one of the most notorious murders in this country in recent years. They describe how Tony Blair’s office would regularly ask for updates on the investigation; how officers themselves were moved to tears by Sarah’s death and how a tip-off from the public gave them the all-important breakthrough.

Detective Inspector Paul Williams tells the programme that Roy Whiting immediately came under suspicion but had to be released due to a lack of evidence.

Using footage from police interviews and detailed accounts from senior officers, the film tells of the efforts to gather the proof needed to charge Whiting with Sarah’s murder following the discovery of her body in a shallow grave 17 days later and 15 miles from where she disappeared.

Detective Supt Peter Kennett, who led the hunt for Sarah’s killer, describes the discovery of her body as “one of the saddest days ever”.

Ray Chapman, one of this country’s leading forensic scientists, tells the programme how a shoe handed in by a member of the public turned out to be crucial in securing Whiting’s conviction. The shoe was sent for testing and fibres from one of Whiting’s jumpers were found in its Velcro strap.

On February 6th 2001 Whiting was arrested and charged. Sara Payne describes the moment she came face to face with her daughter’s killer in the courtroom.

She says: “I was about to see the man who had murdered my daughter. I threw up about two or three times in the morning. I had had nightmares for I don’t know how long.

“And when he came up from the cells and he was this little, dirty, unkempt man that wasn’t a monster, that wasn’t this thing that I could possibly be scared of in my life. And I knew that… the only reason that that man picks on children is because there is no way an adult would have him anywhere near.”

She also describes how she felt when he was found guilty and she discovered he had indecently assaulted a child before.

She says: “I know that there are bad people out there. I know that it was a case of you know, wrong place, wrong time for her. What I was absolutely devastated and what really knocked me flying was the fact that he’d done it before.

“And I am told constantly that it doesn’t happen very often but I’m constantly reminded that if it only happens to one child it is too many.”

Wednesday, 25 June 2008, 9:00PM - 10:00PM ITV1