Texas officials prosecuted Ms. Brown anyway. Their reasons were never made clear, but they may well have been rooted, Ms. Brown’s supporters say, in their feelings about her social class, her former profession and the color of her skin.

“Criminal cases sometimes acquire a momentum of their own, and sometimes there’s an attitude that we find: ‘Don’t confuse me with the facts. I’ve got my mind made up,’” Mr. Strickland, the lawyer, said. “You always want to hope that it’s either in the bad old days or that it’s a Hollywood plotline. But sometimes it’s not.”

Ms. Brown’s trial began in October 1980. As if in a cosmic reminder of the very ubiquity that had landed her there in the first place, a deputy in the trial court was also named Joyce Ann Brown, D Magazine, a Dallas publication, reported.

The prosecutors’ theory of the crime was that Ms. Brown, whom co-workers described as having worn a black blouse and white skirt that day, had slipped out of her office, changed into the blue jogging suit, driven the three miles to the Danzigers’ shop, committed the robbery, changed back into her office clothes, made the three-mile return trip and gone back to work — all in her 36-minute lunch break.

“Because they had a weak case, they bolstered their case with dishonesty,” Mr. Strickland said. “The dishonesty was that the prosecutor put on as a witness a lady whom his office had previously prosecuted for giving false testimony. And he withheld that disquieting fact from the defense.”

That witness was the fourth, and most damning, link in the chain.

The witness was Martha Jean Bruce, a cellmate while Ms. Brown awaited trial, who testified that Ms. Brown had admitted the crime to her. What the prosecutor, Norman Kinne, did not mention was that less than a year before, in an unrelated case, Ms. Bruce had pleaded guilty to making a false statement to the police.

At the time of Ms. Brown’s trial, Ms. Bruce was in prison for attempted murder. Though she said on cross-examination that she had received no inducement to testify, her sentence was commuted shortly afterward.