By a 7-1 vote, the justices struck down a Georgia Supreme Court ruling denying Timothy Foster appellate review of his death sentence. Conservative Justice Clarence Thomas, the court's only African American member, dissented.
"This means that Timothy Foster is entitled to a new trial at which jurors are not excluded based on race," his lawyers said in a statement.
The decision, coming nearly 30 years after Foster's death penalty conviction, highlighted the continuing effect of racism on jury selection in the United States.
The notes, which were obtained after Foster's 1987 conviction, included a list of prospective jurors that had the handwritten letter "B" next to the names of African Americans on the list.
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Those designated with a "B" were rejected for the jury under a selection process that allows prosecutors to block, or "strike," a certain number of potential jurors.
Foster's lawyer told the court that the prosecutors drew up a list of six prospective jurors to be stricken from the panel: five were black, and one was opposed to the death penalty.
"The sheer number of references to race in that file is arresting," he wrote.
The state of Georgia had vehemently defended the prosecutors, arguing that they had documented their actions in order to show they were being thoughtful and not discriminatory in considering prospective black jurors.
But the court's majority said that the state's argument "reeks of afterthought," noting it had never been raised before in the case's 30-year history.
"In addition, the focus on race in the prosecution's file plainly demonstrates a concerted effort to keep black prospective jurors off the jury," Roberts wrote.
The court's decision reverses a Georgia state supreme court order denying Foster appellate review of his death sentence, and remands the case "for further proceedings not inconsistent with this opinion.