How do you stop a sex offender?

Naming and shaming, 'Sarah's law', tougher sentencing - Robert Verkaik asks: can any of these measures really prevent paedophiles from offending again?

The day after Roy Whiting was found guilty of the brutal murder of Sarah Payne, another paedophile in another court was being convicted for child-kidnapping offences. Anthony Knowles, 40, was jailed for six years for "walking off" with a boy and a girl in Liverpool after he befriended them while they were playing in the street.

Although the children were both returned safely, like the lessons of Sarah Payne, the Knowles case highlights the fundamental problem of dealing with paedophiles who reoffend. After the jury at Liverpool Crown Court had found Knowles guilty, the court heard that he also had previous convictions for child abuse. Worse still, he had been free for only 17 days when he committed the offences. Jailing him for six years, Judge Nigel Gilmour said Knowles was a danger to young children and a psychiatric report put him in the highest risk category for such crimes.

In the post-Sarah Payne climate, the Parole Board, probation service and the police will look very carefully at sex offenders before returning them to the community, asking themselves whether they are capable of doing what Whiting did. The fear of being accused of failing to act to protect an abused or murdered child will undoubtedly mean those dealing with convicted paedophiles will err on the side of caution.

The same will be true in the cases of hundreds of other sex offenders who each week are either being convicted by the courts or released from prison back into the community. Judges, too, will want to avoid the kind of criticisms visited on Judge John Gower who sentenced Whiting to fours years imprisonment for child abuse and kidnap six years ago. He found himself on trial by the media because he did not throw away the key.

The Association of Child Abuse Lawyers and child welfare groups argue that more needs to be done to train judges and others who are involved in trying paedophiles. But hindsight is a wonderful thing. Judge Gower, now retired, stands by his decision. On being told that Whiting had been found guilty of the murder of Sarah Payne six years after he accepted a psychiatric report that concluded Whiting did not have "paedophile tendencies", Judge Gower defended his original sentence: "I passed upon him a sentence which in my judgment was warranted in light of the mitigation that was offered to me. The defence, as far as I know, did not appeal the sentence and the Attorney General did not refer it to the Court of Appeal for being unduly lenient."

However, he added that he would need to refer to the original "Whiting case file", which he said contained "material which was not in the public domain", to give a proper account of the sentence he handed down on that day. This, he said, he was not prepared do because judges should not have to justify their decisions outside the context of the courtroom in which they were made. "Otherwise there would be a considerable dent to the independence of the judiciary," he warned.

Judges are also confined by sentencing guidelines and the expert medical reports that are given to the court. And Whiting pleaded guilty to both offences, which must result in a less severe sentence.

Gower was an experienced judge and by the time he passed sentence on Whiting in 1995 he had dealt with dozens of other sex offenders. In 1994 he had jailed a schoolteacher for five years after the man admitted sexually molesting teenage pupils. The court was told how Mark Kent, a single man from East Sussex, had admitted molesting six boys over a seven-year period and had asked for two similar indecent assault charges to be taken into consideration.

In 1996, a year after the Whiting case, Judge Gower had first-hand experience of how a committed paedophile can slip through the criminal justice net. The case against Albert Goozee was much more serious than that against Whiting because he had already been sentenced to life imprisonment for the murder of a 14-year-old girl in 1956.

But in 1971 Goozee was freed on licence. When he appeared in Maidstone Crown Court, Judge Gower jailed him for six years for sexually assaulting two girls aged 12 and 13. Judge Gower told 73-year-old Goozee, who was recalled to serve his life sentence earlier in 1996, that those deciding when, if ever, he could be freed should consider his "horrifying" background.

Yesterday, Judge Gower told BBC Radio 4's Today programme that the feeling of the lower judiciary was that the Court of Appeal had not set severe enough sentencing guidelines. He also said that he would not be throwing his support behind "Sarah's law" where the names of paedophiles are made known to the public, although he could see the sense in alerting headteachers when paedophiles moved into the area. The danger from vigilantes, and the fact that a paedophile is much more likely to commit a crime outside their neighbourhood, would make a Sarah's law unworkable, said the judge. "We do not live in a fascist state where people are convicted for crimes they might commit in the future," he added.

The Sarah's law campaign does not have the support of the police. The Association of Chief Police Officers have made it clear that officers were still mindful of what happened in Portsmouth after the News of the World published the names of paedophiles. The attacks by vigilantes on innocent people, including a pediatrician, not only led to more crime but also to an additional call on police resources. Instead of deploying officers to monitor potentially dangerous paedophiles in the community police forces were busy guarding vulnerable victims of the vigilante campaigns.

The News of the World has tacitly acknowledged that it might have got it wrong when last year it published the details of dozens of paedophiles. On Saturday the paper's campaign included the names of six paedophiles who had failed to comply with their obligations under the Sex Offenders Register.

Like many paedophiles, Anthony Knowles was living in a bail hostel after being released from his prison sentence. Seventeen days later he tried to "walk off" with two children, gripping one firmly by the hand. He was arrested only after the girl recognised him when she was out in her father's car driving near their home. The police went straight to his hostel and picked him up. Under Sarah's law, paedophiles can expect vigilante groups to be waiting for them as soon as they arrive in the community. If that had happened in the case of Knowles he may have decided to find somewhere else to live, out of sight and free from the attentions of the law.