Just how they rehabilitate murderers, other sexual offenders, and who not. People change over time. The part that doesn't change (for pedophiles) is their attraction to children (unless, well, they intentionally do something like chemical castration or whatever), but that's not their crime, the act is their crime. If an examination by mental health specialists and who not deems they won't commit such crimes anymore, there's no reason at all to keep them locked up. Maybe with certain amount of tracking.