Mr. Roof, 22, stared straight ahead or down at the defense table, avoiding eye contact with witnesses who lost composure on the stand and jurors who sometimes dabbed away tears. When a prosecutor would conclude his gentle questioning, which could draw on for more than an hour, Judge Richard M. Gergel of Federal District Court would call for cross-examination. Mr. Roof, dressed in a cable-knit sweater and slacks, would rise slightly from his seat and announce: “No questions.”

That dynamic has prompted a series of challenges by Mr. Roof, and pointed exchanges between Judge Gergel and David I. Bruck, the veteran, court-appointed capital defender whom Mr. Roof has sidelined, about how much is too much.

“It is not fair to allow that much testimony to be heard by the jury when I am not presenting any evidence — from my family or anyone else — in mitigation,” Mr. Roof argued on Wednesday in a motion that Judge Gergel denied. “If I don’t present any mitigation evidence, the victim-impact evidence will take over the whole sentencing trial and guarantee that I get the death penalty.”

Found guilty in December on 33 counts, including 18 that carry a potential death sentence, Mr. Roof has rejected Mr. Bruck’s strategy of presenting evidence about his background and mental health that might mitigate against his execution. The lawyer has been relegated to the role of standby counsel, allowed to sit beside Mr. Roof and offer guidance but not to question witnesses or to object to the government’s evidence.