Roof, who is accused of killing nine people at a black church in 2015, sought the delay following a mistrial after jurors could not reach a unanimous decision in the Michael Slager case.
-- less than 48 hours before Roof is to go on trial Wednesday -- "is highly likely to create undue pressure on the jury to compensate for the judicial system's apparent failure to punish Mr. Slager by imposing a harsher punishment here," Roof's attorneys said in a motion filed Tuesday.
But US District Judge Richard Gergel would have none of that argument.
"The notion that a prospective juror in this case would respond to a mistrial in a state court case involving a police officer's alleged criminal activity by imposing greater than deserved punishment on a defendant who is alleged to have entered a church building during Wednesday night Bible study and committed completely unrelated crimes seems utterly farfetched and illogical to the court."
Slager, who is white, shot and killed Walter Scott, 50, who is black, after an April 4, 2015, traffic stop. The shooting was captured on a bystander's cell phone video, which showed Scott running away as Slager fired eight times, striking Scott three times in the back. The jury failed to reach a verdict after 22 hours of deliberation.
Gergel on Monday granted Roof's motion to have attorneys assist him during the guilt phase of his trial but act alone during any sentencing proceeding.
But in another order Tuesday, the judge rejected the defense's motion to restart the jury questioning. Gergel wrote that Roof actively participated in jury qualification questioning.
Final jury selection is scheduled for 9:30 a.m. Wednesday.
Roof, who is accused in the June 2015 shootings at Mother Emanuel African Methodist Episcopal Church, was deemed competent to stand trial
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; and nine counts of use of a firearm to commit murder during and in relation to a crime of violence.
If convicted, he could face the death penalty.
Roof also faces nine counts of murder and other charges in the state court system. His trial in that case is scheduled to start in January.