According to the King County, Washington, Medical Examiner's Office, Staley succumbed to a fatal cocktail of heroin and cocaine.
The 34-year-old rocker apparently injected the lethal concoction--known as a speedball or a "Belushi" (after actor John Belushi, who died of a speedball overdose in 1982)--on April 5 and died shortly thereafter, the coroner says. His badly decomposed body wasn't discovered until two full weeks later, found slumped on a couch in his Seattle apartment next to what police described as a heroin kit.
Staley's substance abuse problems were no secret. He documented his drug use in his band's lyrics and discussed his heroin habit in interviews. Alice in Chains disintegrated in 1996, and Staley largely withdrew from public life soon after amid whispers of a worsening addiction.
In a statement following the discovery of his body, his bandmates said, "For the past decade, Layne struggled greatly--we can only hope that he has at last found some peace."
Staley's death is the latest in a string of heroin-related rock 'n' roll demises. He watched fellow Seattle scenester and Nirvana leader Kurt Cobain deteriorate and eventually kill himself after failing to kick his habit; Blind Melon's Shannon Hoon and Sublime's Bradley Nowell also fatally overdosed in the mid-'90s. Staley vowed to stay sober and not wind up like his contemporaries, but he couldn't manage to keep clean.
The singer's family has asked that donations be made to Eastside Recovery Center in Bellevue, Washington.