Associate Justice Clarence Thomas poses for the official group photo at the US Supreme Court in Washington, DC on November 30, 2018.

Justice Clarence Thomas on Wednesday broke his three-year silence at the Supreme Court by asking questions during arguments in a racial discrimination case involving a black man who has faced six trials for a quadruple homicide in the 1990s.

It was the first time that Thomas, the court's only black justice, asked a question since 2016. Before that, Thomas, who was confirmed in 1991, had gone a decade without asking a question.

The case concerns Curtis Flowers, who was convicted of the killing in Mississippi only after five trials either deadlocked or resulted in overturned convictions, including for racial discrimination and prosecutorial misconduct.

The justices are reviewing whether district attorney Doug Evans, who prosecuted Flowers over more than a decade, violated the Constitution by excluding black jurors. Thomas' question concerned whether any white jurors were also excluded.

The justices seemed inclined to rule in favor of Flowers, with even conservative justices appearing disturbed by Evans' conduct. Justice Samuel Alito, a George W. Bush appointee, said that the prosecutor's actions were "troubling."

But in the final minutes of the argument, Thomas, who is often referred to as the court's most ardent conservative, wanted to know if any white jurors had also been struck from the jury.

"Were any peremptories exercised by the defendant?" Thomas asked Sheri Lynn Johnson, Flowers' attorney, referring to challenges to potential jurors.

When she said that there were challenges, Thomas asked: "And what was the race of the jurors struck there?"

Johnson said that the trial attorney defending Flowers had only struck white jurors.

"But I would add that the motive — her motivation is not the question here. The question is the motivation of Doug Evans," Johnson said.

Evans had struck five potential black jurors, leaving only one black juror on the 12-person panel.

Thomas' questions and previous votes suggest that he could vote against Flowers in the matter. Thomas was the lone dissenter in a similar 2016 case, Foster v. Chatman. In that case, the court found that prosecutors had unlawfully struck black jurors from a murder trial of a black man in Georgia.

Thomas has provided a variety of reasons for his reticence to ask questions from the bench. In 2013, he told an audience at Harvard Law School that he thought the justices "should listen to the lawyers who are arguing their case and allow the advocates to advocate."

A decision in the case is expected by late June. Flowers, who is currently on death row in Mississippi, is asking the justices to overturn his conviction.