The responsibility of the victims not to seek revenge is no different from their responsibility not to break any other law. It has nothing to do with how the justice system should treat the prisoner. Otherwise, if you are referring more to the victim's rehabilitation, then you are just changing the perspective, not the question. So let it be the victim who needs rehabilitation before the prisoner is released. For every prisoner there is (or should be) a victim. So you still end up making educated or uneducated guesses about how< rehabilitated the victim must be for it to become practical or ethical to release the prisoner.