“Life without parole sentences share some characteristics with death sentences that are shared by no other sentences. The State does not execute the offender sentenced to life without parole, but the sentence alters the offender’s life by a forfeiture that is irrevocable.  It deprives the convictof the most basic liberties without giving hope of restora-tion, except perhaps by executive clemency — the remote possibility of which does not mitigate the harshness of the sentence….” Justice Kennedy wrote in his majority opinion.

Here is a link to the Graham opinion.