PHOENIX (AP) — The top prosecutor in Phoenix said Wednesday that a decision by Arizona's highest court in favor of a woman who spent more than two decades on death row left him saddened, frustrated and out of options in reviving the case.

Maricopa County Attorney Bill Montgomery discussed the case of Debra Milke at a news conference in which he called the Arizona Supreme Court decision a "dark day" and an injustice to Milke's 4-year-old son. Authorities say Milke dressed her son, Christopher, in his favorite outfit and told him he was going to see Santa Claus at a mall in December 1989 before he was then taken into the desert by two men and shot in the back of the head.

Milke was convicted of murder and sentenced to death, but a federal appeals court overturned the case because of a Phoenix police detective with a long history of misconduct. The judge in the case scheduled a hearing for Monday that could mark the official end to the effort to prosecute Milke, and Montgomery is resigned to defeat.

"There's nothing else that can be done at this point," he said.

Milke, now 51, has remained free on bond since September 2013. Her lawyer, Michael Kimerer, expressed relief after the court decision that the end is finally near after years of legal fights.

The federal appeals court that ruled that prosecutors knew about Phoenix police Detective Armando Saldate's history of misconduct but failed to disclose it. The case rested largely on Milke's purported confession to Saldate, which he didn't record.

Milke has maintained her innocence and denied that she confessed to the killing. The two men who led her child to his death were convicted of murder but refused to testify against Milke.

Prosecutors insist Milke is guilty, but their ability to try her again was limited by the fact that Saldate said he wouldn't testify. He fears potential federal charges based on the U.S. appeals court's accusations of misconduct.