An autopsy on the body of Australian actor Heath Ledger, who has died aged 28, has been found to be inconclusive.
It will take about 10 days to determine the cause of death, a spokeswoman for New York's medical examiner said.
"We have to do additional testing which will include toxicology and tissue testing," the spokeswoman said.
Police said they found prescription pills at Ledger's apartment in New York. The Brokeback Mountain star died there on Tuesday.
Meanwhile, tributes have been paid by family, fans and Hollywood. Father Kim Ledger said the death of his "dearly loved son" was "tragic" and "accidental".
Brokeback Mountain director Ang Lee described working with Ledger as "one of the purest joys of my life".
"He brought to the role of Ennis more than any of us could have imagined - a thirst for life, for love, and for truth, and a vulnerability that made everyone who knew him love him," he said. "His death is heartbreaking."
Fans have been leaving flowers and candles outside Ledger's apartment in the SoHo district.
Khaled Ali, a 41-year-old Broadway stage manager, left a candle and said: "I felt a connection with him as an actor, as a fellow in the theatre community.
"With Brokeback Mountain he touched me personally in telling the story of my community. It was very touching."
President George W Bush has postponed an event to promote an advertising campaign on preventing prescription drug abuse.
"We felt it would be better not to hold the event today given the tragedy of yesterday's passing of the beloved actor," White House spokeswoman Dana Perino said.
"We did not want anyone to think we were trying to link into that story in any way."
Ledger, who earned an Oscar nomination for his role in Brokeback Mountain, was found in the rented apartment at 1526 (2026 GMT) on Tuesday.
In September, the Perth-born actor split from his girlfriend Michelle Williams, with whom he has a two-year-old daughter, Matilda.
Williams played Ledger's wife in the 2005 film Brokeback Mountain.
On Wednesday, Williams and Matilda left Trollhattan, Sweden, where she had been filming.
The actress' father Larry Williams said the worst thing about Ledger's death was that Matilda would grow up without knowing her father.
"My heart goes out to everyone in his family and my family. The saddest thing is his daughter whom he just loved dearly," he said.
Ledger was seen in London last week shooting his latest film, The Imaginarium of Doctor Parnassus, directed by Terry Gilliam.
The star also plays The Joker in yet-to-be-released Batman film The Dark Knight.