The ruling was 6-3 along conservative-liberal lines.

“Dzhokhar Tsarnaev committed heinous crimes,” Justice Clarence Thomas wrote for the majority. “The Sixth Amendment nonetheless guaranteed him a fair trial before an impartial jury. He received one.”

The justices’ ruling reversed a federal appeals court that had wiped away the death sentence for Tsarnaev and ordered a new penalty-phase trial. At the time, the lower court said that Tsarnaev would remain in prison for the rest of his life for an “unspeakable brutal act,” but that the trial court had made mistakes regarding issues related to pretrial publicity, as well as the exclusion of evidence that might have helped Tsarnaev’s case.