A vigilantes' charter? The bitter legacy of Megan's Law

The mother of William Elliott insists her son was 19 and his girlfriend just two weeks shy of her 16th birthday when the couple had sex - behaviour about which people may have differing opinions, but which in the state of Maine was enough to earn him a conviction for statutory rape.

The information about the couple's ages was not available when a vigilante, Stephen Marshall, went online to search for registered sex offenders to kill. Instead, he simply read that in 2002 Elliott pleaded guilty to two charges of sexual abuse of a minor and had served four months in jail. Marshall was also able to access his complete address.

In the early hours of 16 April this year, armed with that information and two handguns, Marshall drove to Elliott's home in the small town of Corinth and shot him dead. The same night, he visited the house of 57-year-old Joseph Gray - also registered on the sex offenders list - and killed him as his petrified wife stood helplessly by.

"My son was not a paedophile," Elliott's mother, Shirley Turner, said. "He shouldn't have been labelled like that. All he wanted to do was to love that girl and make a family. [Without the registry] he'd still be alive today. I'd still have him."

The Home Secretary, John Reid, is currently considering new legislation in Britain to make information about registered sex offenders available to the public - introducing a version of what is known in America as Megan's Law. Meanwhile, here in the US - where the Home Office minister Gerry Sutcliffe is due to see Megan's Law in operation - a contentious debate is continuing about the wisdom and the effectiveness of making such potentially explosive information publicly available.

US public law 104-145 - the legislation commonly known as Megan's Law - was passed by the federal government in 1996 and required law enforcement authorities in each state to make information available detailing the names, addresses and identities of registered sex offenders. Each of the states operates the process differently, deciding for themselves what amount of information to provide to the public and how best to make the information available. Some states, for instance, only make available information about the most dangerous offenders, while in Maine everyone convicted of a sexual offence is listed.

Some states even have their own additions to Megan's Law. In Wisconsin, for instance, there is Amie's Law, named after a young woman, Amie Zyla, who was eight years old when she was attacked by a repeat sex offender. The original Megan's Law - which persuaded the federal government to introduce state-wide legislation - was introduced in New Jersey after the rape and murder of seven-year-old Megan Kanka in 1994. Her parents, Maureen and Richard, still live in the same street in Hamilton Township from which their daughter was lured into the house of a registered paedophile, Jesse Timmendequas. Her body was discovered the following day in a nearby park.

Inspired by the impassioned campaign by Mrs Kanka, who two days after her daughter's death vowed that no other little girl should be killed by a sex offender, the legislation was designed to empower parents by giving them information about such convicted people. This information, it was argued, would allow parents to take better precautions to keep their children safe, despite studies that show the overwhelming majority of offenders are not strangers.

But in the past few years, the debate about whether or not to make such information available has taken on a new intensity after the murder and attempted murder of registered sex offenders by vigilantes who obtained their names, addresses and conviction details simply by clicking on the internet.

In addition to the two April killings in Maine by Marshall, 20 - who turned his .45 calibre Magnum on himself when police cornered him near Boston - two sex offenders were killed last year in Bellingham, Washington state, by a vigilante posing as an FBI agent. Meanwhile, in New Hampshire, a man is in jail for the attempted murder of two other registered sex offenders in 2003.

Critics say that while Megan's Law may be well intentioned, there is a real danger of making the information about offenders too easily available to all.

"This is the only law I have seen that causes more violence than in prevents," said Jack King, a spokesman for the National Association of Criminal Defence Lawyers. "There are a lot of versions. Some make sense and will only provide the block number of a dangerous, repeat offender. But some states don't differentiate if someone was caught urinating behind a pub and was convicted of indecent exposure."

Mr King said the system in operation in Massachusetts has four tiers, with information made available only about more serious sex offenders. He said that Mrs Turner's son may have been convicted of a sexual offence, but not a sexually violent offence. "Did that man belong on a sexual predator list? I would hope that [the British parliament] will consider some of the mistakes that the states have made," he said.

Charles Onley, a research associate with the Centre for Sexual Offender Management, a non-profit group, said the four murders were the only fatal crimes he knew of that had been carried out during the approximately seven years in which most states have made their offender registries publicly available. "In the last couple of years more information has been available on the internet," he said.

But there is widespread evidence that other registered sex offenders have suffered violence and - much more commonly - harassment and abuse. A study carried out in Florida and published last year in the Journal of Contemporary Criminal Justice found that a third of convicted male sex offenders sampled had experienced "dire events". The study found that only 5 per cent had suffered assaults or injuries, but that the 33 per cent who said they had suffered negatively had typically undergone the "loss of a job or a home, threats of harassment or property damage". It added: "Some participants noted positive effects of Megan's Law, including motivation to prevent reoffence and increased honesty with friends and family."

Janice, the wife of Joseph Gray, says that her husband had always been honest with her. When they married a decade or so ago, she knew about his 1992 conviction for the indecent assault, battery and rape of a child. She declined to speak about the specifics of his offence, but said "it was not what it sounds".

Speaking yesterday from her home near Bangor, Maine, she told The Independent how she had seen Marshall shoot her husband. "I saw Mr Marshall standing at my window at 3am. I saw him execute my husband," she said, detailing how her husband had died in her arms after he was hit by two bullets.

After the killings, it emerged that Marshall had travelled to Maine from his home in Nova Scotia, Canada, with the names and addresses of 29 sex offenders obtained from the internet that he had saved on his laptop. The night he killed Gray and Elliott he had driven to the homes of four other registered sex offenders living in north-east Maine.

Mrs Gray does not argue that her husband should not have been registered, though she says it was wrong that such information is so easily available. She suggests such information should be held by police, who could then perform checks on people who request details of convicted offenders.

"The politicians think it's fine to put it on the internet. [But] this is going to keep happening," she said. "My husband was a good man. Everyone who knew him said that. He had one bad incident."

Defenders of Megan's Law say that while making information about sex offenders available carries risks, providing such details can often be the only way parents can protect their children.

No one has been more active in pushing for this information to be available than Maureen Kanka. Unknown to the Kankas, three convicted paedophiles were living together in a property just yards from their home. Among them was Timmendequas, who had twice been convicted of child molestation.

On the evening of 29 July 1994, it was Timmendequas - working on his boat parked in his driveway - who lured Megan into his house as she passed by on her bicycle. He told her he had a puppy that he wanted her to see.

Instead, Timmendequas sexually assaulted the little girl, strangled her to death, abused her again and then dumped her body in a nearby park. The following day, questioned by police as to Megan's whereabouts, Timmendequas was asked if Megan might still be alive. "No, she's dead," he replied. "I put a plastic bag over her head." Mrs Kanka and her husband have worked tirelessly to prevent other families suffering as they did. Their organisation, the Megan Nicole Kanka Foundation, campaigns to prevent crimes against children.

"You can't have any more need than a need for something like that. It should have never happened," she subsequently told the New Jersey Express-Times. "My daughter was across the street. That's where she was killed - right across the street. I thought it was safe for my kids to play in the neighbourhood and it wasn't." She added: "The police department never knew three paedophiles were in the neighbourhood. There was nothing in the law to tell them. Now there is."

Another woman who would agree with Mrs Kanka is Amie Zyla. Now aged 18 and having recently graduated from high school, the teenager was eight years old when she was assaulted by a neighbour, Joshua Wade, six years her elder. The boy was convicted of a minor offence and then sent to a treatment centre until the age of 18.

It was in January 2005 that Ms Zyla was watching the local television news that she learned that someone had been arrested for molesting teenagers. It transpired that Wade, then 23, was working at a summer camp but although the camp had done a background check, there was nothing on his record about his juvenile convictions because it had been wiped clean when he turned 18.

Helped by her father and local politicians, Ms Zyla ensured the passage of Amie's Law, which allows police to make public the records of juvenile sex offenders if they are deemed a danger.

Speaking yesterday from Waukesha, Wisconsin, Ms Zyla explained what drove her to act. "I did not think it was fair - he did this to me and then he did this to all these other people," she said. "I was really mad. I was really mad."