There are a few different... criteria. Are they capable of feeling remorse? Some people truly aren't. Is it possible to make restitution for the things they did? Some crimes are too heinous and wanton. Though, I guess... maybe the Barge is making me reconsider that notion. That there's a level of psychopathy where redemption isn't possible. Though I'm not sure there are Earthbound institutions capable of delivering what the Barge does.