In a 5-4 ruling today, the U.S. Supreme Court upheld a lower court order that could require California to release tens of thousands of inmates.

Here's a copy of the opinion which concludes that California has failed to correct serious constitutional violations in its prison system caused by overcrowding.

"Overcrowding has overtaken the limited resources of prison staff; imposed demands well beyond the capacity of medical and mental health facilities; and created unsanitary and unsafe conditions that make progress in the provision of care difficult or impossible to achieve," Justice Kennedy wrote in the majority opinion, which was joined by the court's liberal bloc.

WSJ's Jess Bravin reports that the ruling upholds the findings of a special three-judge district court that has been overseeing California prison litigation for years.

The suit traces to 1990, alleging that California prisons were denying inmates the minimally required level of mental health treatment, according to Bravin, who notes that California's efforts to cure the problems were deemed insufficient, due to severe overcrowding that has seen its penitentiaries swell to nearly double their intended capacity of 80,000.