Megan Kanka, aged seven, was raped and strangled after she followed a neighbour and his puppy into his house on July 29th, 1994.
The neighbour, Jesse Timmen dequas, dumped her body in a park but later showed it to police. In October he was charged with murder, kidnapping and sexual assault.
When it was revealed that he was already a convicted sex offender, the population of Hamilton, New Jersey, was outraged that Megan's parents had not been told that a dangerous sex offender lived on their street.
Two weeks later the New Jersey legislature rushed through a package of bills, which became known as Megan's Law. It required convicted sex offenders to register with local authorities once they are released from prison.
One of the laws also allowed police to notify neighbours if a potentially dangerous offender lived or worked among them.
In June last year Timmen dequas was sentenced to death and is still on Death Row. But in the meantime, Megan's Law was challenged as unconstitutional by sex offenders in New Jersey, while other states rushed to pass similar legislation.
The US Congress passed a federal law on similar lines in May 1996 and it was signed by President Clinton. Again there were constitutional challenges.
One point concerned whether such laws should apply to people sentenced for sex offences before the laws were in operation. Did this not mean that such people were receiving "added punishment" after they had already been sentenced and served their prison term?
Estate agents worried that they could be liable for negligence if they sold a house on a road where a convicted sex offender lived and did not inform the buyer.
Megan's Law has been upheld in appeals courts in the past few years and is now widely in operation in the US. Some states even put the registry of sex offenders on the Internet.
Each state has varying laws with the same basics, which is a compulsory register of sex offenders and availability of this information depending on how high-risk the offenders are.
In New York, for example, sex offenders must register with local police within 10 days of release and annually for the next 10 years, giving details of address and movements, with photographs and other identification.
Those classified as "violent predators" must register every three months and even after 10 years may have to keep registering indefinitely, depending on what a court decides.
The police in areas where these offenders live can make the information available in various ways to the local population.
In California, after the first year of implementation, 64,580 "serious" sex offenders were registered, of whom 1,640 were "high-risk". The register is distributed on CD-ROM to police forces by the Department of Justice. There are 213 public viewing sites where people can consult the CD-ROM.
In addition, police distributed 6,500 leaflets profiling high-risk offenders and have notified schools of over 200 specific offenders. The Sex Offender Identification Line has had almost 8,000 inquiries, resulting in 421 identifications of serious and high-risk sex offenders.