In Montgomery v. Louisiana (2016), the United States Supreme Court ruled that its holding in Miller v. Alabama (2012) “that a juvenile convicted of a homicide offense could not be sentenced to life in prison without parole absent consideration of the juvenile’s special circumstances” — “is retroactive to juvenile offenders whose convictions and sentences were final when Miller was decided.” The facts of the case are as follows: When Montgomery was seventeen years old, he killed a deputy sheriff in Louisiana. Upon his conviction of murder, he was sentenced to life in prison without the possibility of parole. “That sentence was automatic upon the jury’s verdict, so Montgomery had no opportunity to present mitigating evidence to justify a less severe sentence.” After Montgomery had spent nearly half a century in custody, the Supreme Court ruled, in Miller, that in light of children’s “diminished culpability and greater prospects for reform,” the imposition of mandatory life without parole on juvenile homicide offenders violates the Eighth Amendment’s prohibition of “cruel and unusual punishments.” Montgomery then sought collateral review of his mandatory sentence in the state courts of Louisiana. The Louisiana Supreme Court ruled that Miller was not retroactive to cases on state collateral review. Montgomery challenged that ruling in a petition for certiorari.
In the present decision, the Supreme Court asserted “that Miller announced a substantive rule of constitutional law,” i.e., a rule that “forbids ‘criminal punishment of certain primary conduct’ or prohibits ‘a certain category of punishment for a class of defendants because of their status or offense.’” In concluding that such a rule must be applied retroactively to cases on state collateral review, the Court opined that a state judicial system “has no authority to leave in place” an unconstitutional conviction or sentence, “regardless of whether the conviction or sentence became final before the rule was announced.” The Court noted that in Teague v. Lane, it had mandated the retroactive application of new substantive rules of constitutional law in federal habeas proceedings. The Court reasoned that if, in light of a new substantive rule, “a State may not constitutionally insist that a prisoner remain in jail on federal habeas review,” then “it may not constitutionally insist on the same result in its own post-conviction proceedings. Under the Supremacy Clause of the Constitution, state collateral review courts have no greater power than federal habeas courts to mandate that a prisoner continue to suffer punishment barred by the Constitution.”