(01/20/19)- Three years after the U.S. Supreme Court offered a second chance to some 2,000 juvenile lifers, about 400 have been freed and hundreds more have shortened sentences.

But most remain behind bars as the justice system wrestles with some very difficult cases.

Tensions have mounted and lawsuits have been filed in some states; in others, courts and lawmakers have moved to permanently ban life without parole for juvenile offenders.

The high court's 2016 decision hinged partly on research showing the brains of adolescents are slow to develop, making teen offenders likelier to act recklessly but capable of rehabilitation.

The court said they must not be punished with the same finality as adults, and that a life-without-parole sentence should be reserved for those inmates deemed beyond rehabilitation.