Will Megan's Law protect our kids?

It was the early hours of April 16 last year as he pulled up outside the home of Joseph Gray. Gray, 57, had been convicted for the indecent assault and rape of a child in 1992. He lived with his wife, Janice, who knew about his conviction, in Maine, America.

At 3am, Janice woke to find Marshall standing by her window, just before he fired two bullets into her husband.

Joseph Gray was one of two men to die that night. Earlier, Marshall had driven to the home of 19-year-old William Elliott, who had been convicted of a sexual offence after having sex with his girlfriend two weeks shy of her 16th birthday.

When police cornered Marshall, 20, in Boston he turned the gun on himself.

Gray and Elliott are just two victims of violent deaths since the introduction of Megan's Law in America, the law which allows people to know whether there's a paedophile living in their midst. Two sex offenders in Washington state were killed last year by a vigilante posing as an FBI agent.

The four deaths are the most high-profile cases of violence since the introduction of Megan's Law, but it is harder to pinpoint other instances of vigilantism, given that it can range from a demonstration with placards to a house being daubed with graffiti.

Now the law may be heading to British shores - albeit on a scaled down level.

Megan Kanka was seven when she was killed by convicted child molester, Jesse Timmendequas on July 29, 1994. He lured her from her house in a quiet suburb of New Jersey on the pretence of seeing a puppy and raped and murdered her just metres from her home. It later emerged that Timmendequas had served six years in jail for aggravated assault and attempted sexual assault on another child.

Two days after her daughter's death, Maureen Kanka launched a campaign arguing that parents should have a right to know whether a sex offender was living among them. As the weeks went by, almost 500,000 people signed a petition demanding a change in the law.

Within three months, the State of New Jersey had passed Megan's Law. It was adopted in some form by all 50 states in May 1996.

Mrs Kanka is in no doubt as to its success.

"It has been very effective," she says. "For the public, it's been a tremendous tool because it provides an awareness they otherwise would not have had."

But while the law may have helped some parents feel more secure, there has been controversy about its effectiveness and whether or not it encourages sex offenders to go underground.

One of the chief complaints centres around the way different states interpret the law. Each state in America decides what information to provide to the public and how best to make the information available. Some states only give details of high risk offenders, whereas others, such as Maine, list everyone convicted of a sexual offence. It means that some offenders have been forced to post a scarlet 'M' in their window, or tell their neighbours of their offences. A judge in Texas reportedly told 14 paedophiles to display signs in their gardens stating: 'Danger! Registered sex offender lives here!' and bumper stickers in their cars which read: 'Danger! Registered sex offender in vehicle!' In Louisiana, one company offers email alerts warning residents if a paedophile is about to move in, while in Washington, police can call at homes in any given neighbourhood, informing residents of the arrival of an offender.

In her report entitled Megan's Law: Does It Protect Children? for the children's charity, NSPCC, Kate Fitch says that most states have "very little evidence" on the impact of notifying the community about sex offenders. She says there needs to be more research to find out whether there have been fewer assaults by strangers on children (currently there is no evidence that this is the case) and on vigilantism against offenders.

"Although there are few known incidents of harassment, it is likely that these crimes are under-reported and under-recorded," she writes.

"Fears remain about the potential for offenders to 'go underground'. In many cases where a warrant has been issued, states rely on offender traffic violations or 'sweeps' where they attempt to locate missing offenders. Both have limited results."

She points out that the biggest threat to children is often found in the home, not from strangers, and that Megan's Law could end up detracting attention from more common abuse in the family. She says some victims who live with their abusers may be put off reporting the crimes if they know a family member will be denounced. There is no provision under Megan's Law to protect the identity of the victims.

The law has received prominence in this country since the murder of Sarah Payne in 2000. Sarah was abducted and killed by convicted paedophile Roy Whiting as she played with her brothers and sister near their grandparents' home in West Sussex. It later emerged that Whiting had convictions for sexually assaulting a nine-year-old girl.

In December, the Home Office revealed plans for "targeted two-way disclosure" in which members of the public could ask officials for information about child sex offenders. Last night, following an outcry by children's charities, it appeared that the plans would stop short of allowing people to know if there was a sex offender living in their street.

Home Office sources said it wanted people to request information on people they were concerned about, but it did not want details of offenders to be made widely available. Single mothers, for example, would be entitled to know if a new partner was on the sex offenders' register.

Earlier yesterday, Middlesbrough-born Martin Narey, chief executive of the charity Barnardo's, said he felt the introduction of a Megan's or Sarah's law would cause many sex offenders to flee supervision. "The best way of supervising sex offenders, if they are not in jail, is to keep them under the most meticulous supervision," he said.

"If they are serial sex offenders, to have them curfewed, to have them subject to lie detector tests, to have staff observing them every single day. If they flee that, then they become very dangerous indeed."

In America, Joseph Gray's widow does not argue that her husband should not have been on a sexual offenders' list, but says it is wrong that the list is so widely available. She told one newspaper: "The politicians think it's fine to put it on the internet. But this is going to keep happening. My husband was a good man. He had one bad incident."