An initial autopsy on the body of actor Heath Ledger has returned a inconclusive verdict.
The Brokeback Mountain star, 28, was discovered unconscious at his apartment in SoHo in downtown Manhattan, New York, at around 15:30 local time (20:30 GMT) yesterday.
New York City police were reportedly investigating the possibility that the Hollywood star died of a drug overdose, although it seems an official verdict may be delayed by up to ten days.
"We have to do additional testing which will include toxicology and tissue testing," a spokeswoman for the New York medicxal examiner's office said.
Ledger had been due to have a massage at the Broome Street apartment when his housekeeper discovered him unconscious on Tuesday afternoon.
"He was found unconscious at the apartment and pronounced dead," police spokeswoman Paul Browne said.
"We are investigating the possibility of an overdose," he told the Reuters news agency.
"There were pills within the vicinity of the bed."
The Perth-born actor received an Oscar nomination for his role in Ang Lee's Brokeback Mountain in 2005 but Philip Seymour Hoffman took the award for his acclaimed role in Capote.
Ledger met his partner, Dawson's Creek actress Michelle Williams, on the set of Brokeback Mountain, with whom he had a daughter, Matilda.
The couple separated in September last year.
Ledger starred in I'm Not There, as one of several actors representing Bob Dylan, and had recently completed production on his role as the Joker in the upcoming Batman movie The Dark Knight.