Heath Ledger as the Joker in The Dark Knight. - Photo courtesy Warner Bros image:36868:1::0

Because it was inconclusive, the autopsy suggests that his death was caused by substances rather than a disease. Toxicological tests take time, which is why the public must wait for an answer.

Ledger was found dead in his Manhattan apartment yesterday by his housekeeper. He was naked and face down on the floor. Rumors are circulating that the 28-year-old died of a drug overdose as pills were found near the bed. No note was left, and there were no signs of foul play.

Fans are mourning the death, leaving mementos on the street outside his apartment. His former fiancé, Michelle Williams and their 2-year-old daughter are returning from Sweden due to the news.

Condolences are also coming from Hollywood. Fellow Australians Mel Gibson and Nicole Kidman have both released statements.

Ledger’s final film, the latest in the Batman series, is schedule to release in July, with him playing The Joker. The role apparently challenged and disturbed Ledger. He reported having problems sleeping during the last few weeks of filming.

Ledger might be the second young actor to die from a drug overdose this year. On January 15, 25-year-old Brad Renfro was found dead in his Los Angeles home. His cause of death also has yet to be determined; however, he had a history of drug and alcohol abuse and possession.