PHOENIX (Reuters) - An Arizona woman who spent more than 22 years on death row was expected to be released on bail on Friday to await a new trial on accusations she conspired to kill her 4-year-old son a few days before Christmas in 1989. Maricopa County sheriff's officials said Debra Milke, now 49, was expected to walk out of a Phoenix jail and into a waiting car once lawyers post bond of $250,000, in the latest twist in a sensational murder case. In March, a federal appeals court tossed out Milke's conviction and on Thursday a county judge set bail for her. Testimony in her original trial suggested she dressed her son, Christopher, in his best outfit, told him he was going to see Santa Claus at a mall and had her roommate take the boy, in a plot that ended with the man killing Christopher. Milke's roommate, James Styers, picked up his friend, Roger Scott, and instead of heading to the mall, the two men drove to a secluded ravine where Styers shot Christopher three times in the head. Both men were separately convicted of first degree murder and remain on death row. Milke was convicted of murder, conspiracy to commit murder, child abuse and kidnapping in 1990. But in March, the U.S. 9th Circuit Court of Appeals found prosecutors failed to disclose a history of misconduct, included lying under oath, by the detective who solicited a purported confession by Milke. Testimony by Phoenix police detective Armando Saldate, who said Milke confessed to her role in the crime, was considered to be the singular key to her conviction. During the trial, Saldate said Milke told him she had contemplated having an abortion while pregnant with Christopher, had complained to Styers about her son, and confessed to conspiring to the murder. But the admission was not recorded, nor was anyone else in the room when it was purportedly made. Milke denied making any confessions and has continued to maintain her innocence. On Thursday, Judge Rosa Mroz of Maricopa County Superior Court set bail for Milke and said Saldate's history "casts serious doubts on the validity of the defendant's alleged confession." A hearing was scheduled for September 23 to determine if evidence of Milke's confession was "valid and admissible." It was unclear if Saldate will testify in the retrial. A lawyer for Milke could not immediately be reached on Friday and a spokesman for prosecutors declined comment. Editing by Cynthia Johnston and Grant McCool