Staley, 34, lay dead in his north Seattle apartment for two weeks, his body surrounded by heroin-injection paraphernalia, before a relative discovered him, authorities said Sunday.
Foul play was not suspected, and there was to be no criminal investigation, Seattle Police spokesman Duane Fish said.
``There was nothing suspicious about the death. It appears to be overdose or possibly a natural death,'' Fish said.
Staley's body was reported found Friday, but the presence of drug paraphernalia and estimated time of death were not initially released. An autopsy was conducted on Saturday, but the cause of death would not be confirmed for as long as four weeks while toxin tests were being conducted by a state lab, the King County Medical Examiner's office said on Sunday.
Some 100 friends and fans held an impromptu candlelight vigil Saturday night at the Seattle Center.
Behind Staley's snarling, wailing vocals, and Jerry Cantrell's driving guitar riffs, Alice in Chains became one of the biggest acts to emerge from the Seattle grunge phenomenon of the early 1990s, with Nirvana, Soundgarden and Pearl Jam. The group's debut, Facelift, got significant national airplay, and its 1994 EP, ``Jar of Flies,'' debuted at No. 1.
The group's hits included ``Man in the Box,'' ``Them Bones,'' ``Rooster,'' and ``Would?''
The latter song was partly inspired by the 1990 heroin overdose death of Andrew Wood, singer of the early grunge group Mother Love Bone, some of whose members would go on to form Pearl Jam.
Staley made no secret of his heroin addiction. He was featured on the cover of a 1996 issue of Rolling Stone with the heading ``The Needle and the Damage Done.'' Several of the songs on Alice in Chains' album ``Dirt'' dealt with heroin addiction.
The band was essentially in limbo by 1995, as Staley fell deeper into addiction. He spoke of making a comeback, but the band never again launched a major tour.
Alice in Chains was known for its dark, morbid lyrics, most penned by Staley and Cantrell. In ``Confusion,'' Staley wrote and sang: ``Love, sex, pain, confusion, suffering / You're there crying, I feel not a thing / Drilling my way deeper in your head / Sinking, draining, drowning, bleeding, dead.
Another song from 1990's ``Facelift,'' ends abruptly with the line ``And we die young.''
Staley entered rehab several times but couldn't kick his habit.
His body was found eight years after troubled Nirvana frontman Kurt Cobain was found dead in his Seattle home of a self-inflicted gunshot wound. Heroin was found in Cobain's bloodstream.