Lisa Robin Kelly Death Still a Mystery

8/17/2013 12:45 AM PDT BY TMZ STAFF
Lisa Robin Kelly
's autopsy is complete ... but cause of death is still unknown, TMZ has learned.

A spokesperson for the L.A. County Coroner's Office tells TMZ, the autopsy was finished Saturday -- but the cause of Lisa's death won't be known until the toxicology results are in ... which could take weeks.

As TMZ previously reported ... The "That 70's Show" actress died in her sleep Wednesday night while staying at a treatment center for alcohol abuse. A few days prior she had been admitted to the hospital by her boyfriend with a BAC of .34 (borderline fatal).