Kelly Burke took a few labored steps to the witness stand and looked toward a large video screen in a rural Georgia courtroom. There, he saw the face of a man, beamed in from a nearby prison, whom he had sent away 25 years earlier for life without parole.

Mr. Burke, a former district attorney, hadn’t seen the man, Jessie Askew Jr., since the sentencing in 1998. He had insisted at the time that Mr. Askew, then 24 years old, deserved to die in prison. On this spring morning in 2023, Mr. Burke planned to tell the court it was the biggest mistake of his career.

Both men had changed since then, though Mr. Burke’s transformation was more dramatic. Once an imposing 6-foot-7, he was now a hunched cancer patient who relied on a motorized wheelchair. Complications from the disease had left him thin and unable to swallow. And he was deeply troubled by a self-inflicted wound to his conscience.

“Good morning, Mr. Burke,” Mr. Askew said, representing himself because he couldn’t afford a lawyer. “Would it be fair to say you remember my case?”

“Very much,” said Mr. Burke, whose trouble swallowing caused saliva to build up, making him at times hard to understand.

Mr. Askew was hoping to persuade a judge to overturn his sentence for an armed robbery in 1997. Mr. Burke was his only witness.