[4] According to Human Rights Watch, children as young as 9 have been placed on the registry;[5][6] juvenile offenders account for 25 percent of registrants.

[11] C. Don Field was prompted by the Black Dahlia murder case to introduce a bill calling for the formation of a sex offender registry; California became the first U.S. state to make this mandatory.

Prior to 1994, only a few states required convicted sex offenders to register their addresses with local law enforcement.

She believes that by not allowing sex offenders who have served their time to reintegrate to society we do more harm than good, "I've turned 180 from where I was."

[16] In 1994, 7-year-old Megan Kanka from Hamilton Township, Mercer County, New Jersey was raped and killed by a recidivist sex offender.

Jesse Timmendequas, who had been convicted of two previous sex crimes against children, lured Megan in his house and raped and killed her.

Megan's mother, Maureen Kanka, started to lobby to change the laws, arguing that registration established by the Wetterling Act was insufficient for community protection.

In 1996, President Bill Clinton enacted a federal version of Megan's Law, as an amendment to the Jacob Wetterling Act.

The AWA was signed on the 25th anniversary of his abduction; efforts to establish a national registry was led by John Walsh, Adam's father.

SORNA requires states to widen the number of covered offenses and to include certain classes of juvenile offenders.

Scholars have warned that classification system required under Adam Walsh Act is less sophisticated than risk-based approach previously adopted in certain states.

[3][13][20] Extension in number of covered offenses and making the amendments apply retroactively under SORNA requirements expanded the registries by as much as 500% in some states.

[21] All states were required to comply with SORNA minimum guidelines by July 2009 or risk losing 10% of their funding through the Byrne program.

[13][neutrality is disputed] As of April 2014[update], the Justice Department reports that only 17 states, three territories and 63 tribes had substantially implemented requirements of the Adam Walsh Act.

Depending on state, registration and notification systems may have special provisions for juveniles, habitual offenders or those deemed "sexual predators" by virtue of certain standards.

Some states, like Massachusetts and Colorado, utilize multidisciplinary review boards or judicial discretion to establish registrant tiers or sexual predator status.

In addition, hundreds of counties and municipalities have passed local ordinances exceeding the state requirements,[31][32] and some local communities have created exclusion zones around churches, pet stores, movie theaters, libraries, playgrounds, tourist attractions or other "recreational facilities" such as stadiums, airports, auditoriums, swimming pools, skating rinks and gymnasiums, regardless of whether publicly or privately owned.

[33][34] In a 2007 report, Human Rights Watch identified only four states limiting restrictions to those convicted of sex crimes involving minors.

[35] Restrictions may effectively cover entire cities, leaving small "pockets" of allowed places of residency.

[48] Majority of research results do not find statistically significant shift in sexual offense trends following the implementation of sex offender registration and notification (SORN) regimes.

In fact, a number of negative unintended consequences have been empirically identified that may aggravate rather than mitigate offender risk.

Consequently, the study found that a majority of the public endorses broad community notification and related policies.

[56][57] Critics of the laws point to the lack of evidence to support the effectiveness of sex offender registration policies.

Critics say that registries are overly broad as they reach to non-violent offenses, such as sexting or consensual teen sex, and fail to distinguish those who are not a danger to society from predatory offenders.

[58][59][60] Former Supervisory Special Agent of the FBI Kenneth V. Lanning argues that registration should be offender-based instead of offense-based: "A sex-offender registry that does not distinguish between the total pattern of behavior of a 50-year-old man who violently raped a 6-year-old girl and an 18-year-old boy who had 'compliant' sexual intercourse with his girlfriend a few weeks prior to her 16th birthday is misguided.

[62] These perceived problems in legislation have prompted a growing grass-roots movement to reform sex offender laws in the United States.

Those challenging the statutes have claimed violations of ex post facto, due process, cruel and unusual punishment, equal protection and search and seizure.

[66][67] In September 2017 a federal judge found that the Colorado registry is unconstitutional under the cruel and unusual punishment clause of the United States Constitution as applied to three plaintiffs.

[68] Sex offender registration and community notification (SORN) laws carry costs in the form of collateral consequences for both sex offenders and their families, including difficulties in relationships and maintaining employment, public recognition, harassment, attacks, difficulties finding and maintaining suitable housing, as well as an inability to take part in expected parental duties, such as going to school functions.