Woman's conviction overturned after 22 years on death row

An Arizona woman's conviction has been overturned after she spent 22 years on death row for the murder of her 4-year-old son.

A U.S. Circuit Court of Appeals ruled that Debra Jean Milke's 1979 murder conviction could not stand because a detective who testified against her in her trial had an undisclosed history of misconduct.

According to prosecutors, Christopher was killed by two men, one of whom was his mother's boyfriend.

They told the boy he was going to see Santa Claus, before shooting him in the Arizona desert.

Christopher Milke was shot in the desert at the age of four. Photo: Supplied

At the time of Milke's trial, the prosecution had argued that the boy's mother was part of a plot to have him killed for insurance money.

The detective in question testified that she had confessed to the crime, but no recording was made of the confession, and Milke always upheld her innocence.

According to the ruling that has saved Milke from death row, Detective Armando Saldate had a history of at least eight cases of lying under oath and violating suspects' rights during interrogations.

He was also suspended for "taking liberties" with a female driver he pulled over and lying about it, ABC News reported.

"Milke's conviction was based largely on the testimony of Police Detective Saldate, who allegedly obtained her confession," the court ruling states.

"The panel held that the state remained unconstitutionally silent instead of disclosing information about Det. Saldate's history of misconduct and accompanying court orders and disciplinary action."

Milke will now be released from prison, unless the prosecution decide to retry her.