Washington (CNN) Nearly two decades after Lee Boyd Malvo engaged in a serial sniper shooting spree that terrorized Maryland, Virginia and the District of Columbia and left 10 dead, the Supreme Court wrestled Wednesday with his sentence of life without parole.

Last year, a Richmond, Virginia-based federal appeals court ordered a new sentencing trial for Malvo, who was 17 when the crimes were committed in 2002, citing two Supreme Court opinions issued subsequent to his sentencing in state courts.

Wednesday, the justices struggled for more than an hour discussing the impact of their own prior cases as well as the details concerning Virginia's sentencing scheme. The case comes after the retirement of Justice Anthony Kennedy, who wrote a landmark opinion in 2005 barring the death penalty for juvenile offenders and could offer the newly constituted conservative majority the chance to cut back on court precedent.

In 2012, the justices held in Miller v. Alabama that mandatory life-without-parole sentences for juvenile offenders violate the Eighth Amendment's ban on cruel and unusual punishment. Four years later, in Montgomery v. Louisiana, the court said the Miller decision applied retroactively.

"To be clear," the 4th US Circuit Court of Appeals said last year, the crimes committed by Malvo "were the most heinous, random acts of premeditated violence conceivable." But the court said it had concluded that even though Malvo's sentence was "fully legal when imposed" it had to be vacated because he "now has the retroactive benefit of new constitutional rules that treat juveniles differently for sentencing."

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