In an 8-1 ruling, the state high court said that Darold Stenson's rights were violated because the state "wrongfully suppressed" photographs that raised questions about mishandling of evidence as well as an FBI file that wasn't provided to the defense until 2009, years after Stenson was convicted.
Stenson was sentenced to death in 1994 for the 1993 slaying of his wife, Denise, and a business partner, Frank Hoerner, at Stenson's Clallam County exotic bird farm.
Sheryl McCloud, an attorney for Stenson, said she was pleased that the court so overwhelmingly sided with their position.
"I was just so gratified that the court was willing to make a decision that might be unpopular but is really necessary given what we discovered almost 20 years after the conviction about the evidence being so unreliable," McCloud said.
The high court noted that other than two key pieces of evidence that tied Stenson to the shootings, the remainder of evidence provided at trial was "largely circumstantial." Those two pieces of evidence - gunshot residue found inside the front pocket of the jeans Stenson was wearing when officers arrived, and blood spatter on the front of those jeans "consistent with Hoerner's blood protein profile" - were at the heart of Stenson's most recent appeal to the high court.
At issue were photographs showing sheriff's Detective Monty Martin wearing Darold Stenson's jeans with the right pocket turned out and Martin's ungloved hands and an FBI file indicating an agent who testified did not perform a gunshot residue test, which the court said was implied at the trial.
Stenson had claimed that he kneeled next to Hoerner's body, accounting for the blood on the jeans. But an expert witness called by the prosecution had testified that was not possible.
"Had the FBI file and photographs been properly disclosed here, Stenson's counsel would have been able to demonstrate to the jury that a key exhibit in the case - Stenson's jeans - had been seriously mishandled and compromised by law enforcement investigators," wrote the majority for the high court, led by Justice Pro Tem Gerry Alexander.
Clallam County Prosecuting Attorney Deborah Kelly said she was deeply disappointed by the decision.
"It is my firm belief that all involved in the investigation and prosecution of this case acted conscientiously and in good faith towards a just outcome. It is an utter tragedy for the victim's family that they are forced to relive this."
Kelly said she expected a retrial on murder charges but would consult with the family about whether to seek the death penalty again.
Stenson has long claimed he didn't commit the murders. When Stenson called authorities in 1993 to report the deaths, he suggested that his business partner, Frank Hoerner, had killed Denise Stenson and then shot himself in another room. Prosecutors have said Stenson, struggling financially and in dire business straits, shot the two in order to collect $400,000 in life insurance.
Stenson has filed multiple appeals to his death sentence, and courts have stayed his execution three times, most recently in 2008 when he was less than two weeks from a scheduled execution.
In January 2011, a Superior Court judge ruled that the prosecuting attorney did not meet its legal obligation to provide the evidence to the defense but also found it wouldn't have changed the outcome of the trial, something the high court disagreed with in its ruling Thursday.
The high court noted that it had already once affirmed both of Stenson's convictions and the death sentence in 1997, and has since rejected four prior personal restraint positions filed by Stenson.
But the current petition cited due process violations of the so-called Brady rights. Those rights are named after the Supreme Court's Brady v. Maryland case, which says prosecutors violate a defendant's constitutional rights by not turning over evidence that could prove a person's innocence. The high court on Thursday said that those rights were violated.
"We are left with the fact that constitutionally significant mistakes were made in Stenson's trial, resulting in imposition of the ultimate punishment without the full benefit of due process protections," the majority opinion read.
Alexander was joined on the majority in Thursday's ruling by Chief Justice Barbara Madsen, Justices Charles Johnson, Debra Stephens, Tom Chambers, Charles Wiggins, Mary Fairhurst and Justice Pro Tem Teresa Kulik.
Justice Jim Johnson, the lone dissenter, argued that the Supreme Court has "reviewed and affirmed both guilt and sentence over the intervening 18 years" since Stenson was sentenced.
"The interests of finality in justice to provide peace for the families of Stenson's victims argue for the same result," he wrote.
With Stenson's death sentence now overturned, seven men remain on death row at the state penitentiary. Washington state's last execution was in September 2010, when Cal Coburn Brown died by lethal injection for the 1991 murder of a Seattle-area woman. He was the first Washington inmate executed since 2001, after spending nearly 17 years on death row.
Since 1904, 78 men have been put to death in Washington.