What was the legislative basis for enacting Megan's Law:
The theory of recidivism -or- actual recidivism statistics?
The history behind Megan's law. It started in New Jersey with three terrible high profile rapes and murders of little girls, Divina Genao, Amanda Wengert and Megan Kanka, in August of 1993, and, May and July of 1994. The offenders, Conrad Jeffrey, Kevin Aquino and Jesse Timmendequas, all had a history of sex crimes; recidivists. It is unknown whether any of these offenders --successfully completed-- any sex offender therapy program while in prison, but it begs the question why were they released?
In 1979 Jesse Timmendequas pled guilty to assaulting a 5-year-old girl, and he was given a suspended sentence which he failed to complete and ultimately spent 9-months in a correctional center. Then in 1981 Timmendequas was again arrested for assaulting a 7-year-old, he pled guilty and was sentenced to 10 years at New Jersey's Adult Diagnostic and Treatment Center (ADTC) for sexual offenders. He was paroled in 6-years with time off for good behavior. In 1992 he moved in with Joseph Cifelli, a sex offender whom he met at ADTC, whose mother owned the home and was an Alzheimer's victim, and another sex offender Brian Jenin also lived there, it was here Timmendequas murdered Megan Kanka. 
Megan's parents felt, if they had known a sex offender was living in their neighborhood, their daughter would not have been killed. They started a petition and presented it to their legislature, which enacted New Jersey's Megan's law by October of 1994; all in 94 days. the New Jersey legislature based Megan's law on recidivism of these offenders.
There is a general belief that, all sex offenders have a high rate of recidivism, that belief existed in 1994 as well; the truth is, that is a myth!  Interestingly, in 2003 the Department of Justice actually calculated the recidivism rate for all sex offenders, using 1994 figures, and found that it was 3.5% as to another sex offense. The basis of these registry laws has proven to be false, yet the myth continues.
While the legislature jumped on the issue of recidivism (the theory of recidivism), the legislature ignored the issue of how these men got back into society. A little known fact about the 1994 New Jersey parole system is, that annually, 60% of their --parole eligible-- inmates, were actually granted paroles; a very high rate.
Departments of Justice reports  show, in 1994 in New Jersey there were 700 parolees per 100,000 adult residents, that dropped in 1998 to 238 per 100,000 residents, and again in 2002 to 183 per 100,000 residents. Clearly New Jersey recognized there was something wrong with their parole system and took steps to tighten the system without publicizing it. Statistics now show their parole rate dropped from 60% to approximately 26%, the major portion between 1994-1998. Jeffrey, Aquino and Timmendequas were all released during that 60% period. Their civil commitment law was enacted in 1999.
The belief that, "if the public knew where sex offenders lived, then they could protect their children," came from the fact that the Megan Kanka crime was actually committed in the home of the offender. History has proven that, no other high profile sex crime involving a child, has had that characteristic. The Divina Genaro and Amanda Wengert crimes were not committed in the homes of those offenders.
The New Jersey legislature, in 94 days, still went ahead and enacted what has come to be known as, Megan's law. Local New Jersey prosecutors have even commented that, had Megan's law been in place before that crime, it would not have saved Megan, because the law would not have given the community notice given Timmendequas' history. 
When laws affect fundamental rights, the state is supposed to tailor the law, to achieve the compelling state interest, and using the least restrictive means. There is no question regarding the compelling state interest, children, however, there are serious questions about using the "Theory-of-Recidivism" rather than "Actual Recidivism Statistics" upon which to base this law.
Everyone needs to question their state legislature:
1) What is their state meaning of "sex offender recidivism," it should be a sex offense followed by another sex offense? (ReArrest -or- ReConviction?)
If legislatures were forced to answer these questions, they could not support the passage of their Megan's law under the theory of Public Safety... Legislatures will circumvent these questions, and never answer them, because to answer them truthfully would expose the myth behind "High Sex Offender Recidivism" and destroy the basis of Megans' laws!
2) Why has the legislature failed to base their Megan's Law on "sex offender recidivism rates" of --state-- sex offenders who have been previously placed on parole and probation?
3) Precisely what "sex offender recidivism statistics" did the legislature consider to support passage of Megan's Law??
4) As to the specific recidivism statistics the legislature did rely upon: a) were these statistics of just a sub-group of sex offenders and are now being applied to the class of sex offenders; b) did these statistics include only convictions for sex offenses (i.e., meaning, other crime types, or technical violations of supervision which should be excluded); c) if statistics were based upon a mental health study or research, was it cross-validated by someone other than the developer; and d) were the statistics based upon fact or a hypothetical premise.
Will legislature ever admit the error of Megans' laws?
10:.. Doe -v- Poritz, Supreme Court of New Jersey, 7-25-1995: Attorney General of New Jersey, in brief filed in this case, stated "As Doe acknowledges, successful treatment of sex offenders appears to be rare. He correctly notes that very few offenders sentenced to ADTC [Adult Diagnostic and Treatment Center ever [***21] meet the dual standards required for parole from ADTC. Indeed, according to Department of Correction's statistics between 1980 and 1994 only 182 inmates were paroled from ADTC. While plaintiff was among [*16] the few who were released as 'capable of making an acceptable social adjustment in the community,' the large majority of ADTC inmates leave only after having served their maximum sentences. During the same time frame, 1980 - 1994, 712 inmates were released from ADTC at expiration of term.
[Response Brief for Attorney General at 6-8 (citations omitted).]" The successful completion of therapy was not a requirement of parole back then. (Pre-civil commitment laws)
11:..Recidivism of sex offenders released in 1994. Washington, DC: Bureau of Justice Statistics Special Report, Langan, P. A., & Levin, D. J. (November 2003). (40 pg PDF) reported that, 3.5% of sex offenders (men who had previously committed a rape or sexual assault) were RECONVICTED for another sex crime within 3 years following their release.
Parole 1994: Bureau of Justice, Adults on Parole 1994, Table 6.2 (New Jersey 700);
Probation and Parole in the United States, 1998: Bureau of Justice, Adults on Parole 1998, Table 5 (New Jersey 238);
Probation and Parole in the United States, 2002: Bureau of Justice, Adults on Parole 2002, Table 5 (New Jersey 183).
13:.. Court TV Library "New Jersey v. Timmendequas (5/97)."; Court TV Crime Library "Whispers and Rumours."
14:.. -- "Mental health professionals also said the overall risk of molesters reoffending is lower than the public perceives." Article by, By Gideon Gil, The Courier-Journal, and several mental health professionals including Dr.Fred Berlin.
-- "But as the Court itself noted, the Scale is not to be considered infallible. Contrary to common misperception, not all sex offenders are at high risk of recidivating; possibly even some rated as high by the Scale. Rather surprisingly, a 1996 United States Justice Department release found sex offenders to be amongst the lowest of recidivists when compared to other serious offenders. In that particular study, over 90% of sex offenders residing in the community on probation had not recidivated. " Court Testimony by Dr. Fred Berlin.
-- "In a recent phone interview, Dr. Fred Berlin, a researcher, clinician and teacher at the Sexual Disorders Clinic at Johns Hopkins University, said that "overall" an estimated 35 percent of untreated offenders commit new crimes. After weekly cognitive-behavioral therapy over a series of months, the number drops to around 15 percent. ..." Dr. F. Berlin in interview with Salon.com on their article "Out of the Frying Pan, into group therapy, page 4."
15:.. Court TV "In a Child's Name," ----What's more, many offenders had been convicted or pleaded guilty in the past to less serious offenses, crimes that did not rise to the level of Megan's Law notification. Notably, the name Jesse Timmendequas, Megan's killer, would not have been publicly released if the sex offenders’ registry had existed at the time of the girl's death. His prior offenses would not have warranted widespread community notification. A popular saying among prosecutors in New Jersey's 26 counties is, "Megan's Law would not have saved Megan." ----