Michael Mullen, Sex Offender Vigilante

As Duncan sits in jail in Idaho on murder and kidnapping charges, some experts are citing his case as an example of the false promise of the country's sex offender registries and the plethora of new laws intended to rein in the behavior of sexual psychopaths like Duncan.

Duncan is one of 550,000 registered sex offenders in America. Broken down by state or city, the numbers seem staggering: 63,000 in California, 22,000 in New York, 5,200 in Oklahoma, 2,000 in Sacramento, 1,300 in Seattle. Full-time monitoring of each of them is not economically viable.

Instead, the felons are identified through sex-offender registries and, in some cases, public notification when the offender moves in to a new neighborhood.

Some question the effectiveness and common sense of that policy.

John La Fond

John La Fond, a retired law professor in Tacoma who has researched America's treatment of sex offenders, told the Crime Library that Web publication of offenders' names and addresses "almost becomes a confession by the state that they cannot keep the society safe from harm. It invites society to take matters into its own hands."

One Washington state man, in a blue rage over Duncan's crimes against the Idaho family, is accused of doing just that.