A preliminary autopsy on Heath Ledger today was unable to determine what killed the actor. The New York City medical examiner's office will conduct additional toxicology and tissue tests which will take from 10 days to two weeks to complete.
At this time there no obvious indicators of what killed Heath and nothing to contradict initial police reports that the death was not a suicide.
The fact that initial tests were inconclusive suggests his death was caused by substances in his system rather than diseased or damaged organs, according to New York-based forensic psychiatrist Dr. Michael Welner.
During an autopsy, Welner said, medical examiners are "looking for mechanisms of disease; the diseased heart, diseased lungs." These investigations take less time to complete than toxicological tests, which could reveal effects of drugs and other subtances on the body.
[source: ABC News]