Prison should be both a place of reform and a place of punishment. In my opinion, for the act of premeditated murder, of willingly taken another human life, the punishment should be the removal of the possibility of living out any of the remainder of your life a free man/woman.
I think you're getting too caught up in thinking prisons should be based solely around reforming those that have already committed crimes that you forget it's also meant to dissuade those considering committing a criminal act, something that I think removing the future possibility of parole does more effectively than keeping that possibility in place. It may be to a relatively small effect, but if it prevents only a few murders a year, I'd say it's worth it.
“It is a strange paradox that today’s central banks are generally staffed by economists, who by and large profess a belief in a theory which says that their jobs are, at the best, unnecessary, and more likely wealth-destroying. Needless to say, this is not a point widely discussed among respectable economists. Nevertheless, it is an issue worth pondering.”
George Cooper, The Origin of Economic Crises