CHARLESTON, S.C. (Reuters) - A federal judge on Monday postponed jury selection in the U.S. death penalty trial of the 22-year-old white man accused of shooting nine people to death at a historic black church in Charleston, South Carolina, last year.

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U.S. District Judge Richard Gergel instead held a closed hearing involving only defendant Dylann Roof and his lawyers, to discuss issues in the case. No proceedings have been planned on Tuesday because of Election Day.

Roof, who is accused of holding white supremacist views, faces 33 federal counts of hate crimes, obstruction of religion and using a firearm in a violent crime after he opened fire during a Bible study session at Emanuel African Methodist Episcopal Church in June 2015.

The final phase of jury selection was to begin on Monday at the U.S. courthouse in Charleston.

Gergel said he did not know the full subject matter of Monday’s closed hearing, but that issues remaining in the case included contested evidence. He said Roof’s rights would be prejudiced by an open hearing.

“It’s necessary to do it right,” Gergel said in court.

Prosecutors said the victims’ relatives were frustrated at being shut out of the hearing, having waited so long for the trial.

Dozens of family members had been seated in the courtroom on Monday before the surprise announcement. Roof sat at the defense table, wearing a gray and white striped prison jumpsuit.

The case is unfolding as another racially charged trial progresses across the street. Michael Slager, a white former police officer in North Charleston, is on trial for murder in state court in the shooting of black motorist Walter Scott in April 2015.

The two incidents, which occurred two months apart, shook the country and further intensified the debate over U.S. race relations.

Roof has offered to plead guilty if the death penalty were dropped, court filings show.

He also faces a death sentence if found guilty of murder in state court in a trial scheduled for next year.

Prosecutors say Roof planned the church attack for months, singling out victims who were black and elderly, and say that he showed no remorse. At the federal trial, they plan to present racist manifestos they say he wrote in an effort to incite a race war.