Darcus Allen was convicted of four counts of aggravated murder for his role in the cold-blooded November 2009 shooting. He appealed, arguing that a prosecutor misstated the legal definition of "knowledge" when he accused Allen of knowing that Maurice Clemmons planned to shoot the officers.
Allen drove Clemmons to the scene, waited and drove him away. Clemmons was killed two days later in a confrontation with a Seattle police officer.
The original sentencing judge arrived at the 420-year sentence by giving Allen 100 years in prison for each officer who was killed, plus 20 years for use of a firearm in the killings, to be served consecutively.
Killed were Sgt. Mark Renninger and officers Tina Griswold, Greg Richards and Ronald Owens.
Allen has maintained all along that he had no idea Clemmons was going to kill the officers, and that he constantly prays for their families.
"I'm sorry about what happened to your family. If I could have stopped it, I would have stopped it. I had no idea that this man was going to kill your family members - and that's the honest-to-God truth," he said during earlier court proceedings.
But jurors didn't buy that and convicted him.
Six other people were also convicted of assisting Clemmons in the killings, but one of those convictions was later thrown out by an appeals court.