EDWARD LEE ELMORE turned 53 in January. For more than half his life, the soft-spoken African-American who doesn’t understand the concept of north, south, east and west, or of summer, fall, winter and spring, was in a South Carolina prison, most of it on death row.

On Friday, Mr. Elmore walked out of the courthouse in Greenwood, S.C., a free man, as part of an agreement with the state whereby he denied any involvement in the crime but pleaded guilty in exchange for his freedom. This was his 11,000th day in jail.

Mr. Elmore was convicted in 1982 for the sexual assault and murder of an elderly white widow in Greenwood. His trial lasted only eight days, including two spent picking the jury. The state concealed evidence that strongly pointed to Mr. Elmore’s innocence and introduced damning evidence that appears to have been planted by the police. For three decades lawyers for Mr. Elmore, who were convinced of his innocence, sought to get him a fair trial.

Headlines and news stories about men being released from death row based on DNA testing suggest that this happens often. But it doesn’t. Once a person has been convicted, even on unimaginably shaky grounds, an almost inexorable process — one that can end in execution — is set in motion. On appeal, gone is the presumption of innocence; the presumption is that the defendant had a fair trial. Not even overwhelming evidence that the defendant is innocent is necessarily enough to get a new trial. “Due process does not require that every conceivable step be taken, at whatever cost, to eliminate the possibility of convicting an innocent person,” Justice Byron R. White wrote for the majority in a 1977 case, Patterson v. New York.