Bradford, now 42, is set to die by injection Wednesday evening in Huntsville for the robbery-slaying more than 22 years ago.
"If you saw it once, you wouldn't forget it," said Dan Hagood, a former Dallas county assistant district attorney who prosecuted Bradford. "That video was just so chilling. That man's begging for his life. He's got his hands up.
"Then: Bam! ... Like stepping on a bug."
The U.S. Supreme Court last week refused to reconsider Bradford's appeal, clearing the way for the fourth execution this year in Texas and the first of four set for this month in the nation's busiest capital punishment state.
No last-day appeals for Bradford were planned, his lawyer, Mick Mickelson, said Tuesday.
"He's going to be executed," Mickelson said.
Bradford was 20 at the time of the Dec. 29, 1988, shooting at the store a few miles south of downtown Dallas, and was on parole for a robbery conviction.
In a confession to police, he contended that he acted in self-defense, that his gun went off and he feared Williams was trying to get his own gun and shoot him. The video, however, contradicted his version of the shooting.
Edwin King Jr., one of Bradford's trial lawyers, recalled the video as "very disturbing, and when the jurors saw it most of them began to cry."
His co-counsel, Paul Brauchle, said the tape showing Williams in prolonged agony was devastating to the defense trying to keep Bradford off death row.
"The jury gets to sit there and listen to the guy moan and groan and agonize," Brauchle said. "A 4-year-old kid could have gotten death."
Bradford had two trials. His first conviction in 1990 was thrown out by the Texas Court of Criminal Appeals, which ruled that the trial judge in the case improperly denied psychiatric testimony obtained by Bradford's lawyers. He was tried a second time in 1995, convicted and sentenced again to death.
Last October, he won a Supreme Court reprieve about a week before he was scheduled for execution when his attorneys argued that his trial court appointed an inexperienced and underqualified lawyer to handle some of his earlier appeals. In January, the justices rejected the appeal. Last Friday, they refused to reconsider their decision.
Court records showed Bradford, who told a psychologist he began drinking alcohol in the seventh grade and had about four or five beers daily, was building a criminal record even before he went to prison for robbery. Police told of dozens of contacts with him on the streets of Dallas, where Bradford was known as "G-Man." One woman testified how he slipped into her home and tried to get into her bed before running off when she alerted her stepfather.
Other testimony at his trial showed that while in prison on the robbery conviction he incited one riot and was involved in another.
Police who arrested Bradford for the Williams slaying found marijuana and guns in his room. Detectives who booked him found he was carrying two plastic bags of crack cocaine.
Bradford told jurors most of the trial testimony against him came from liars.
Earlier appeals rejected by the courts contended he was mentally impaired and ineligible for execution.
Bradford declined to speak with reporters as his execution date neared. His accomplice, Vandron Seymore, received 42 years in prison for aggravated robbery with a deadly weapon. He served 12 years and was paroled in 2002.