The Supreme Court has ruled that a previous decision that put an end to automatic life sentences without parole for juveniles should be retroactive.

The 6-3 ruling means that some 2,100 juvenile murders will now have the possibility of parole.

As NPR's Nina Totenberg reported, this case was a "procedural spiderweb." But the implications of it were easy to understand: At issue was whether a previous ruling by the high court applied to Henry Montgomery, who killed a police officer in 1963 when he was 17-years-old. Montgomery was sentenced to life in prison without parole.

But back in 2012, the Supreme Court decided that sentencing youth to life without parole amounted to cruel and usual punishment. That rule obviously applied to all future cases, but what about past cases?

The Supreme Court resolved today that it did indeed have jurisdiction to review this case and that its previous ruling was substantial enough that it should apply retroactively.

Here's how Justice Anthony Kennedy concluded the majority opinion:

"Henry Montgomery has spent each day of the past 46 years knowing he was condemned to die in prison. Per­haps it can be established that, due to exceptional circumstances, this fate was a just and proportionate punishment for the crime he committed as a 17-year-old boy. In light of what this Court has said in Roper, Graham,andMiller about how children are constitutionally different from adults in their level of culpability, however, prisoners like Montgomery must be given the opportunity to show their crime did not reflect irreparable corruption; and, if it did not, their hope for some years of life outside prison walls must be restored."

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