Lie detector shows offenders' contact with kids

The news came as the probation service confirmed it had begun trials in polygraph testing on sex offenders.

Probation chief Eithne Wallis said the machines could have a future role in monitoring the likes of paedophiles, if further tests proved their reliability.

Prof Grubin, who is based in the Sexual Behaviour Unit at Newcastle University, said he was now in talks with the Home Office over a possible larger trial involving up to 200 offenders.

The trial was carried out by two American polygraph examiners on sex offenders in the West Midlands, Northumberland and Surrey last year.

Offenders were all on probation and were asked a series of questions about their past offending, current behaviour and fantasies.

They were asked if they had been in contact with children or on the look-out for victims.

Prof Grubin said: “Everyone disclosed information relevant to their rehabilitation.

“About a third revealed unsupervised contact with children and with three of them, we believe, if intervention had not been taken, they would have reoffended.

“The men themselves said as much afterwards, in retrospect, if action had not been taken.”

Of the three cases, one man was put back in a hostel, child protection proceedings were started in another and the third had his supervision increased, Prof Grubin said.

Polygraphs are widely used in America, including the monitoring of sex offenders but also in criminal investigations, custody evaluations and professional sexual misconduct cases.

Police departments have even been known to use them in pre-employment checks.

However, the use of the machines is still at a very early stage in this country and doubts over their accuracy mean they cannot currently be used by police and are not accepted as evidence in the courts.

But talking about more research, Ms Wallis said: “If it worked and if there was a robust, demonstrable level of reliability it may be that there would be a place for that as a piece of supporting information in our management of sex offenders.”

Prof Grubin, a forensic psychiatrist, wants to set up a two-year scheme in three probation areas and compare the findings with three areas where polygraphs are not used.

A spokeswoman for the Home Office said it was too premature to give any indication of future development of last year’s trial.

She added: “We are looking at the results of the experiment and said any development would be investigated.

“The National Probation Service is constantly looking at developments that might assist it in its protection of the public and clearly it would be remiss to discount anything.”

Sandy Gray, a polygraph examiner from Arizona, said: “They (paedophiles) are very deviant and usually very skilled at being manipulative.

“By monitoring, the polygraph examination is, by far, better than simply accepting and taking their word for what they are doing.”

But Roger Stoodley, who led the investigation into the paedophile network which included the notorious child killer Sidney Cooke, said he was sceptical of the development.

Sex offenders are practised liars and would be able to fool the most sophisticated equipment, he said.

Prof Grubin said experience in the United States suggested that in 90% of cases, people could not cheat.

Paul Cavadino, chief executive of the National Association for the Care and Resettlement of Offenders (NACRO), said: “The issue of reliability is the key one.

“If it is shown there is a high level of reliability it would be perfectly reasonable to use polygraphs as part of the supervision and monitoring of sex offenders.”

Roger Bingham, a spokesman for civil rights group Liberty, added: “It seems reasonable to use polygraphs if they are proved reliable.

“However, they should not become a substitute for other safeguards used to monitor such offenders.”