Here's an Associated Press story about Minnesota's decision to lock up indefinitely about 40 sex offenders who have already served their sentences for their crimes. Says Attorney General Mike Hatch:
We have approximately 40 sexual predators who are unable to control their sexual impulses on the street, or about to be on the street, due to the failure of the department to do its job.
The criminals in question are "Level 3" offenders, meaning they have been designated as high risks of committing more sex crimes. (As Thomas Szasz wrote in this Reason article about Catholic priests-pedophiles, it's far from clear whether sex criminals in general are more likely to repeat their crimes).
The impulse to round up such people is totally understandable but it also flies in the face of a criminal justice system predicated upon serving time for past crimes. And it obviously opens up major civil liberties issues–and creates a precedent for proactively locking up other sorts of potential criminals, too. At least 16 states currently allow for the indefinite lockup, typically in mental hospitals, of past sex offenders.
This much is clear: This is as much (or more) a political issue as it is a criminological one. Attorney General Hatch is, says the AP, a "potential Democratic candidate for governor in 2006" and "has accused Republican Gov. Tim Pawlenty's administration of not doing its job or following the law."