Some can be rehabilitated.. perhaps one time murderers?
I don't know, but it seems that once a person has shown that they can use that option to solve their issues for money (murder the robbery victim and/or eye witnesses), sex/control (murder the victim as an eye witness and also out of blood lust), etc, "rehabilitation" would just mean "learn how to play the game better" to them, and "ticking time bomb" to the rest of us.
And no, I do not buy into the old saw that "everyone is a potential murderer and/or rapist." Nonsense.