You can't really read too much into that.
This is not a double blind test.
Those that learned not to kill may well have simply learned to exploit other people in equally nasty if perhaps less lethal ways.
(EG Thompson and Venables. I dont believe for one Atto-second that Thompson is any less of an evil little *** than Venables. It is just at he has bean taught, and has learned, to hide it better. That is not "reformation" and it does not mean he is safe. If he thought he could get away with it he would happily do it again!)