Updated

The case against a woman who spent more than two decades on Arizona's death row in the murder of her 4-year-old son was dealt a crushing blow Wednesday when a judge ruled that a discredited detective won't be forced to testify at her retrial.

A judge granted former detective Armando Saldate's request to assert his Fifth Amendment right against self-incrimination. A purported confession that Debra Milke gave Saldate represents the crux of the case. Without his testimony, prosecutors can't use the confession at her retrial and have little other evidence.

Milke was accused of having two men shoot her son in the desert outside Phoenix in 1989. She spent nearly 24 years on death row before the 9th U.S. Circuit Court of Appeals overturned her conviction in March. The panel cited the prosecution's failure to turn over crucial evidence, saying that deprived her attorneys of the chance to question the credibility of the state's key witness — Saldate, who told jurors she confessed.

Prosecutors declined to comment Wednesday about how the ruling affects their case.

"The court finds that Saldate has demonstrated a reasonable apprehension of danger that, if compelled to answer, he would face criminal charges," Maricopa County Superior Court Judge Rosa Mroz wrote, while also noting she did "not fully agree" with all of the appeals court's allegations against Saldate.

The appeals court cited numerous instances in which the former Phoenix police detective committed misconduct in previous cases, including lying under oath and violating suspects' rights. The court also found that Milke had not waived her right to have an attorney present for Saldate's interrogation of her, something he contended she did.

Saldate did not record the interrogation, so jurors were left with his word alone that she confessed. Milke has maintained her innocence and denied she ever told Saldate she had any part in the killing. The two men convicted in the child's death did not testify against her and remain on death row.

Prosecutors assured Saldate they planned no charges for any wrongdoing. The U.S. Justice Department's Civil Rights Division said it had reviewed the appeals court's allegations and found there wasn't enough evidence to pursue federal charges against Saldate.

However, Saldate's attorney, Larry Debus, argued last week that the federal government's decision "isn't a grant of immunity" and, regardless, it's based solely on the Milke case, leaving Saldate open to prosecution for other instances of misconduct cited by the appeals court.

Judge Mroz agreed, explaining that if Saldate testified again, defense attorneys would question him about the others cases in an attempt to discredit him.

"Depending on how Saldate answers those questions, his testimony could be used against him to support any potential federal criminal civil right charges," Mroz wrote.

The judge also noted that, specific to the Milke case, "each time Saldate testifies against her could be deemed a re-violation of her civil rights."

In addition to finding that Saldate violated Milke's rights, the appeals court cited eight cases in which he committed misconduct. In one 1982 case, the court wrote, Saldate interrogated a suspect who was strapped to a hospital bed and so incoherent he did not know his own name. The trial court later suppressed the statements.

In 1989, according to court records, when the suspect in a killing invoked his right to remain silent, Saldate pushed on with his interrogation. An appeals court later found that violated the suspect's rights.

Judge Mroz noted that if Saldate answers questions under oath related to some of the eight cases, "he may be subject to prosecution under a theory of continuing conspiracy to violation of civil rights" since some of the defendants are still in prison and appealing their convictions.

Milke's attorney, Michael Kimerer, has said if Saldate was allowed to assert his Fifth Amendment right, defense lawyers would likely seek a dismissal of the case based on lack of evidence. He was not immediately available for comment Wednesday.

Saldate has declined comment. His attorney did not return messages.

For now, a retrial is scheduled for 2015 while Milke is free on bond. A hearing in the case is set for January.