As Sarah Payne's killer begins a life sentence, one disturbing question remains.

Why was a sex offender with a recent conviction for abducting a young girl free to pursue his dangerous obsession?

We looked at our top five predatory paedophiles, and he was top of the list

Martyn Underhill Detective Inspector

Roy Whiting's behaviour suggested strongly that he was a man who was not going to change his ways.

Sooner or later, he was going to strike again.

He did so with terrible consequences, ending the life of Sarah Payne and bringing untold misery to her family.

Kidnapping

Whiting was one of the first men in the country to have his name placed on the Sex Offenders' Register, requiring him to keep the police informed about where he was living.

Sarah Payne was not the first girl abducted by Roy Whiting

So it was no accident that the day after the girl disappeared, the police knocked on his door, as Detective Inspector Martyn Underhill explains.

"When Sarah Payne went missing we had to look at our top five predatory paedophiles, and he was top of the list," he says.

Five years earlier, in June 1995, Whiting had stood before another judge at Lewes Crown Court to be sentenced for kidnapping and indecently assaulting a girl aged nine.

The evidence was disturbing. Whiting had attempted to abduct three girls. He succeeded in pulling one into his car and drove off. He told the girl he had a knife, and threatened to tie her up unless she submitted to the assault.

Worrying

Before the case came to court, Whiting was examined by a psychiatrist, who concluded that the mechanic did not have paedophile tendencies.

Jailed: 1995 newspaper report on Whiting

But Brian Clark, of Sussex Probation Service, says there was no doubt about Whiting's potential to repeat the crime.

"The fact that he denied the real implications of the offence was very worrying," he recalls.

"It made the probation service assess him as a high risk offender, and one that could re-offend in the future."

And were probation officers concerned that next time he might kill?

"They were," he says.

Tragic

In court, Whiting's lawyer described his client as living a "Walter Mitty existence" but submitted that the attack was spontaneous and not something he had planned to do.

Seaside: Stalking ground for Whiting

The judge appears to have accepted the argument, telling Whiting: "We sentence you on the basis that it just happened that you had the knife and the ropes in the car, and that this offence was not pre-meditated."

Whiting was given credit for pleading guilty and sentenced to four years in prison.

With remission, he spent less than two-and-a-half years behind bars.

Resources

Whiting's conviction meant that his name automatically went onto the Sex Offenders' Register.

Detective Inspector Underhill, who helped bring Whiting to justice a second time, acknowledges that there are two ways of looking at the case.

Sarah's parents, Sara and Michael Payne

"My view is that the Sex Offenders' Act worked because we knew where he was, and therefore we were able to get to him quickly," he says.

"It didn't save Sarah's life, but it did solve the murder.

"Other people would argue that the Sex Offenders' Act didn't work because we didn't actually stop him committing the offence. But with so many registered sex offenders in Sussex, and in this country, there isn't the manpower or the resources to deal with them."

The case of Sarah Payne inevitably raises questions about a sentencing system that seems to take no account of whether sex offenders respond to treatment in custody, or even whether they agree to be helped in the first place.

Prison kept Roy Whiting off the streets for little more than two years, and did nothing to change his behaviour. He emerged as dangerous as the day he abducted his first victim.

And just as probation officers feared, he struck again...this time with fatal consequences.