Ledger was found dead at his apartment in New York yesterday. The New York Police Department confirmed that drugs had been found in the vicinity of the actor's bed.
A 90 minute autopsy was conducted on Ledger's body this morning, but the results were inconclusive. Tissue and toxicology tests will now be carried out, and the results are expected to be released in "10 days to two weeks''.
A number of Hollywood stars have paid tribute to the actor, who was best known for his role in Brokeback Mountain.