PHOENIX (AP) — Debra Milke was once one of the most reviled mothers around, convicted of dressing her 4-year-old son in his favorite outfit and sending him off to visit a mall Santa Claus with two men who shot the boy execution-style in the Arizona desert.

Milke said she had nothing to do with Christopher's death, but a detective testified at her 1990 trial that she had confessed to him — and him alone — in a closed interrogation room. Prosecutors said she had her son killed to collect on a $5,000 insurance policy.

Now, Milke could walk free, leaving death row behind after a federal appeals court threw out her conviction Thursday because prosecutors had not turned over evidence of the detective's history of misconduct, including lying under oath in other cases.

The 9th U.S. Circuit Court of Appeals panel concluded that prosecutors' failure to turn over the evidence deprived Milke's attorneys of the chance to question Phoenix Police Detective Armando Saldate Jr.'s credibility before jurors.

And because it was the only direct evidence tying her to the killing, that fact could have swayed the jury, the panel ruled.

"No civilized system of justice should have to depend on such flimsy evidence, quite possibly tainted by dishonesty or overzealousness, to decide whether to take someone's life or liberty," according to the opinion by Chief Judge Alex Kozinski.

Barring a successful appeal of Thursday's ruling, prosecutors will have to decide if they have enough evidence to retry Milke. The ruling doesn't toss out the supposed confession. It just allows defense lawyers to have all of the detective's police files.

The ruling has raised questions about other cases in which the now-retired Saldate gave testimony.

The court noted four cases where judges threw out confessions or indictments because Saldate lied under oath and four instances where cases were tossed or confessions excluded because Saldate violated the suspect's constitutional rights.

He was also suspended for accepting sexual favors from a female motorist he stopped and then lying about the encounter, it said.

Saldate, who was elected to a county constable post after retiring in 1990 but has now left that job, could not be reached for comment Friday.

Arizona Attorney General Tom Horne said he intends to appeal the case to the U.S. Supreme Court and will argue it himself if they accept the case, saying the decision was the first to raise the issue after decades of court hearings.

"This is an outrageous crime," Horne said. "Ms. Milke was convicted of arranging for the death of her own child to improve her social life, and I hope to be able to convince the U.S. Supreme court to reverse this 9th Circuit decision."

Maricopa County Attorney Bill Montgomery, who will be charged with deciding whether to retry Milke if the ruling stands, said Friday that he will have to review the available evidence and Saldate's credibility himself before deciding how to proceed. He said there may be more evidence that wasn't used at the 1990 trial.

"I want to know what the hell happened, after reading the opinion," Montgomery said. "I want to be able to review the available information and understand for myself."

But Montgomery said changes in the way rogue officers are monitored had changed greatly since 1990. Now, officers with credibility problems are tracked in a database so that those issues are caught early and disclosed to defense lawyers when necessary.

"The basic concerns that are raised in the 9th Circuit opinion, I do not believe that is anywhere near a systemic issue today," Montgomery said. "This is an instance where I need to make sure what we do is what's right rather than what's expedient."

Phoenix police declined to comment.

Milke's appellate lawyers, Mike Kimerer and Lori Voepel, said the appeals court's decision sends a clear message to police and prosecutors who don't reveal evidence that could help people accused of crimes defend themselves.

"It's one of the most scathing opinions I've ever seen the 9th Circuit write, in terms of talking about the credibility of a police officer or a law enforcement official," Kimerer said. "It almost sets the standard in terms of what we need to expect from law enforcement."

For Milke, who has always maintained her innocence, the ruling after 23 years on death row came as a shock, Voepel said.

"I said, 'Debra, we have good news. We won,'" Voepel said, recalling a phone call Thursday. "And she said, 'you're kidding, you're kidding," and I tried to explain it to her and she said just 'give me a minute here to feel this.' She's elated, to say the least."

Milke, 48, is one of three women on death row in the state.

The two men convicted in the Milke case, Roger Scott and former Milke roommate James Styers, are also on death row. Scott confessed during a police interrogation and led detectives to the boy's body. Neither Scott nor Styers testified against Milke.

The county attorney at the time, Rick Romley, was not so happy. "If she walks, it's a travesty of justice," Romley told KPHO-TV.

Christopher Milke's father, Arizona Mark Milke, was just as adamant, saying he was convinced his ex-wife killed their son.

"Why do you think two guys would just take off and kill my kid," he asked Friday. "Now, if she walks and those two get put to death, that's why this country has gone to hell, brother."

Milke criticized the 9th Circuit for overturning the case after so many other courts upheld his ex-wife's conviction. And he wasn't shy about voicing his views of Saldate.

"There's lot of cops that did good work on this case, but this lead detective, he should never been put on the case," Milke said. "Everything he did was screwed up."