The 22-year-old was convicted last month of the June 17, 2015 killings at the Emanuel African Methodist Episcopal Church.
The 22-year-old was convicted last month of the June 17, 2015 killings at the Emanuel African Methodist Episcopal Church, a historic black church in downtown Charleston known as "Mother Emanuel."
Parishioners attending a Bible study group had just begun their closing prayer when Roof opened fire, unleashing a horrific bloodbath that shocked the nation.
The victims, who had welcomed Roof into the church, ranged in age from 26 to 87.
During the trial, Roof made no attempt to explain his crimes and exhibited no signs of remorse as survivors recounted the rampage in heart-rending detail.
In accordance with federal rules, Roof will appear for sentencing before the same jury that found him guilty of all 33 federal hate crime charges, after just two hours of deliberation.
The twelve carefully selected jurors will decide whether the blond-haired Roof will be imprisoned for life or put to death.
He has elected to represent himself in the proceedings, rebuffing advice from his lawyers and the presiding judge.
The prosecutor intends to bring more than 30 witnesses, including survivors of the carnage and those close to the deceased victims, to the stand.
He will call for the death penalty on behalf of the federal government, based on a law punishing racially motivated crimes.
Capital punishment rarely is meted out in federal cases, in part because violent crimes more typically are tried under state laws.
The last person to be condemned to federal death row was Dzhokhar Tsarnaev, convicted for his role in orchestrating twin bombings at the finish line of the Boston Marathon in 2013.
Federal authorities have executed only three criminals since 1976.
With his life hanging in the balance, Roof could finally play the humility card, expressing remorse or compassion for his victims -- or he could use the court as a platform for racist ideology.
A video of Roof's chilling confession to the killings was shown during the trial's first phase.
"Somebody had to do something because black people are killing white people every day," Roof said without emotion to the FBI special agent questioning him. "They rape 100 white people a day."
Judge Richard Gergel found Roof competent to defend himself in the sentencing phase of the trial, but imposed restrictions on his movements: he will not be allowed to approach the jury, the witness stand or judges.
Roof has told the judge he does not plan to introduce any evidence or witnesses on his own behalf, including any evidence regarding his mental health.
His main defense attorney, renowned death penalty expert David Bruck, had hinted at mental illness in his closing argument, calling on jurors to "look below the surface."
However, he called no witnesses or significantly challenged any of the government's witnesses.
Without Bruck at his side, Roof is at high risk of paying for his crimes with his life.
He could escape the death penalty if just one member of the jury -- ten women and two men -- opposes it.
They are expected to reach a verdict within 10 days.
Roof is also facing state murder charges in South Carolina, in a trial slated to begin January 17. State prosecutors there also are seeking the death penalty.