(CNN) A judge has halted the jury selection process in the Dylann Roof trial to allow time for Roof to undergo a competency evaluation.

Lawyers and US District Judge Richard Gergel on Monday were supposed to start whittling 512 potential jurors down to a manageable number. But Gergel initially postponed the process two days, then said Tuesday that jury selection won't start until November 21, the Monday before Thanksgiving.

Gergel said he was postponing court proceedings because of a motion filed by Roof and his defense team concerning the young man's competency to stand trial. The judge said he would rule on Roof's competency by November 18, CNN affiliate WACH reported

Authorities say Roof, 22, fatally shot nine people at a Bible study meeting at Emanuel African Methodist Episcopal Church in June 2015. Roof said he picked the church, known as Mother Emanuel, because he wanted to provoke a race war. Roof is white and all the victims were black.

Meanwhile, the FBI and Charleston police are investigating a series of letters "referencing racial violence" in Charleston, including one praising Roof, city officials said.

Investigators are trying to determine who sent the series of letters to the Mother Emanuel church, James Island County Park and several hotels, the city's emergency operations center said.

Most of the letters were reported to police last week, and all were sent from outside the US -- including from Canada and the UK.

One of the letters, sent to a hotel, explicitly mentioned Roof:

"Every one of the 9 lives sacrificed by his greatness, Mr Dylann S Roof, is one less I will need to sacrifice," the letter said, according to a police report.

As authorities investigate the letters, Roof is bracing for both federal and state trials.

What happens during the federal jury selection?

Prospective jurors for the federal case will appear in US District Court in Charleston.

The group has been whittled down to 512 from the 3,000 people who received jury summonses, WACH reported.

Groups of 10 were scheduled to gather in the courtroom for questioning until attorneys narrow down the field to 70 for the next stage of the selection process, WACH said. The jurors will be chosen from the Charleston area

When will the federal trial start?

It's unclear when the jury of 12 primary jurors and six alternates will be picked.

According to the Charleston City Paper , the judge said opening statements from prosecutors and defense lawyers might start in late November or early December.

Breaks could be scheduled around Thanksgiving and Christmas. That means the trial easily could carry over into the new year.

What are the federal charges?

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Roof faces 33 federal charges : nine counts of violating the Hate Crime Act resulting in death; three counts of violating the Hate Crime Act involving an attempt to kill; nine counts of obstruction of exercise of religion resulting in death; three counts of obstruction of exercise of religion involving an attempt to kill and use of a dangerous weapon; nine counts of use of a firearm to commit murder during and in relation to a crime of violence.

What is the possible punishment?

If convicted, Roof could be sentenced to death. In announcing its intention to seek the death penalty , the US Justice Department cited several aggravating factors, including Roof's desire to incite violence and picking his victims "in order to magnify the societal impact of the offenses charged in the indictment."

What about murder charges?

Roof faces nine counts of murder and other charges in the state court system. Charleston County Solicitor Scarlett Wilson has said she also will seek the death penalty. The state trial is scheduled to start January 17, 2017, in Charleston.

Who were the victims?

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The shooting victims included the Rev. Sharonda Coleman-Singleton, 45; Cynthia Hurd, 54; Susie Jackson, 87; Ethel Lee Lance, 70; the Rev. DePayne Middleton-Doctor, 49; the Rev. Clementa Pinckney, 41; Tywanza Sanders, 26; the Rev. Daniel Simmons, Sr., 74; and Myra Thompson, 59. Pinckney was a state senator.

How have their relatives responded?

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Citing their Christian beliefs, family members expressed forgiveness in a court hearing days after the massacre. "I will never be able to hold her again, but I forgive you," a daughter of Ethel Lance said. "And have mercy on your soul."

Pinckney's widow, Jennifer Pinckney, has advocated for stricter state gun laws, The Post and Courier newspaper reported . Some family members filed wrongful death lawsuits against the federal government, alleging Roof should not have been able to purchase the gun used in the killings, the newspaper said.

How has the church responded?

Mother Emanuel church, a pillar of Charleston's African-American community since the 1800s, conducted a get-out-the-vote drive ahead of Tuesday's election.

Last July, the church held a one-year anniversary ceremony to mark the killings and designated July 21 Acts of Amazing Grace Day , when everyone was encouraged to perform "their own personal act of amazing grace."

How has the community reacted?

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The jury selection phase coincides with another high-profile, racially charged case -- the trial of former North Charleston police officer Michael Slager , who fatally shot Walter Scott in the back. Slager is white, and Scott was black.

Local ministers, officials and members of the NAACP held a joint news conference October 31 and pleaded for peace during the Roof and Slager trials.