The U.S. Supreme Court has been clear: In decisions, the justices said the harshest punishments levied against adult criminal offenders are unconstitutionally cruel and unusual when imposed on juveniles.

After banning mandatory life without parole for juveniles 17 and younger convicted of homicide, the high court last year said the ruling applied retroactively to the more than 2,000 inmates already serving such sentences nationwide, and that all but the rare irredeemable juvenile offender should have a chance at parole.

Yet for many serving these terms, the ruling's promise of resentencing and a chance at eventual release has so far been halting, inconsistent and sometimes elusive, a 50-state examination by The Associated Press found.