On March 20, 2014, the Illinois Supreme Court ruled that all the inmates currently serving a mandatory sentence of life without parole for crimes committed as juveniles are eligible for new sentences, including sentences of less than natural life.
In 2012, the United States Supreme Court ruled in a case called Miller v. Alabama that mandatory sentencing of juveniles to life without parole constituted cruel and unusual punishment. Since then, state courts have been deciding whether to apply the ruling retroactively to inmates already in prison for crimes committed as juveniles.
This doesn't mean juveniles can no longer be sentenced to life without parole, but that it cannot be a "mandatory" sentence. Mandatory meaning that once someone is convicted of a crime, this is the sentence that must be given. The judge cannot take into account the individual circumstances of the case or the defendant.
The Miller ruling said courts must consider several factors, including the age and maturity of the defendant, before being able to sentence a juvenile to life without parole. The Supreme Court never said whether the requirement was retroactive, which left a big question for Illinois. Did it apply to the approximately 100 juveniles already serving that sentence?
The Illinois Supreme Court has decided that it does. Those inmates should be given new sentencing hearings.