How can you know an abuser (or other criminal) is no longer a threat? Is there a mitzvah of “Pidyon Shvuyim” to get a Jew out of jail when he was convicted of a crime?

Is it possible to determine that an abuser is no longer a risk? What’s the success rate of treating serious abusers?
Why do community leaders sometimes advocate for the early release of an abuser?
How does halacha view cases where a Jewish prisoner receives a disproportionate sentence?
Should the community celebrate someone’s release from prison?