Autopsy, toxicology reports determine Alice in Chains frontman died April 5, two weeks before his body was found.

Alice in Chains' Layne Staley died from a mixture of heroin and cocaine, an autopsy and toxicology report revealed Monday.

Laboratory results determined the singer died April 5, according to a spokesperson for the King County medical examiner's office, the same day fellow grunge pioneer Kurt Cobain committed suicide in 1994. Staley was found dead two weeks later, surrounded by intravenous drug paraphernalia in his Seattle apartment (see "Layne Staley, Alice In Chains Singer, Dead At 34").

The death certificate reads Staley's death resulted from "an acute intoxication due to the combined effects of opiate (heroin) and cocaine." The death was classified as "accidental."

The lethal combination goes by the name "speedball" in drug circles. The same ingredients contributed to the deaths of comedian John Belushi in 1982 and actor River Phoenix in 1993.