Origin of the sex offender registries
Most people think the sex offender registries were only recently established. However, the registry of today is the direct descendant of a program that started in the 1930s. Originally intended to keep Mafia gangsters from setting up shop in Los Angeles, it later became a tool for harassing homosexuals in the McCarthy era. [...]
In the meantime, the country was also experiencing growing anxiety about another kind of crime: sex. A tug-of-war was building between social liberals who viewed consensual sexual activity as a private matter that was no business of the law and moralists who believed that growing sexual license was ruining the society. Military and police operatives began using subterfuge to entrap homosexuals in lewd acts. Consensual homosexual activity between adults was a felony, with long prison terms often followed, in many states, by indefinite civil commitment that could keep the "pervert" locked up for the rest of his life. In 1938, the Los Angeles Police Department established its Bureau of Sex Offenses. The bureau began keeping careful records, with fingerprints and photographs, of sex offenders, and operated a clinic for performing psychiatric evaluations of people arrested on sex charges.
source: 'Origin of the Sex Offender Registries' by Marshall Burns (Ph.D.); www.solresearch.org/~SOLR/rprt/bkgrd/origin.asp; SOL Research; Posted: 26 August 2009; Updated: 7 & 8 September 2009