Accused white supremacist Dylann Roof is mentally competent to stand trial for the shooting deaths of nine black parishioners at a South Carolina church last year, a federal judge ruled on Friday.

Roof's competency was the subject of a 16-hour hearing held behind closed doors on Monday and Tuesday. Earlier this month, defense attorneys had raised concerns for the first time about whether Roof was able to understand the nature of the proceedings against him and to assist in his defense.

U.S. District Judge Richard Gergel said in an order on Friday that he had carefully considered the testimony of a renowned psychiatrist who evaluated Roof, 22, as well as arguments from lawyers.

The judge kept under seal his detailed findings about Roof's competency, saying that making them public would jeopardize the defendant's right to a fair trial.

Jury selection now will resume on Monday.

Roof faces 33 counts of hate crimes, obstruction of religion and firearms charges in the massacre at Emanuel African Methodist Episcopal Church in Charleston, South Carolina, in June 2015.

(Reporting by Harriet McLeod; Writing by Colleen Jenkins; Editing by Bernadette Baum)

Dylann Roof Dylann Roof has been ruled competent to stand trial. He is pictured in court in Charleston, South Carolina, on July 18, 2015. Photo: Getty Images