Tributes pour in for Heath Ledger

An autopsy has failed to reveal whether Heath Ledger, the Brokeback Mountain star found dead in Manhattan on Tuesday, died from an overdose of drugs, possibly accidental. It will now take about 10 days to determine the cause of death, said a spokeswoman for New York's medical examiner. "We have to do additional testing which will include toxicology and tissue testing."

Meanwhile, tributes from the 28-year-old actor's family, fans and Hollywood colleagues have included an ambiguous comment from Jack Nicholson, who famously played the Joker in the first Batman film, the part Ledger plays in the latest in the series, The Dark Knight. Nicholson, hinting that he was aware that the Australian-born actor might have been battling personal demons, said in London: "I warned him".

Ang Lee, director of Brokeback Mountain, the film that made Ledger's name, described working with the Australian-born actor 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."

Ledger's father, Kim, said he was sure the tragic death of his "dearly loved son" was accidental. Larry Williams, father of Michelle Williams, the Brokeback Mountain co-star with whom Heath Ledger had a two-year-old daughter, Matilda, said: "My heart goes out to everyone in his family and my family. The saddest thing is his daughter whom he just loved dearly."

Fans have been leaving flowers and candles outside Ledger's apartment in Broome Street in the SoHo district of Manhattan where his body was discovered.

Meanwhile, Ledger's death has thrown the production of Terry Gilliam's The Imaginarium of Dr Parnassus into confusion and raised questions about the morbid marketing campaign planned for The Dark Knight.

Ledger had just completed a 20-day shoot with Gilliam in London. According to the Hollywood Reporter, the producers of The Imaginarium are now consulting with their lawyers and insurance company to decide whether to recast, restage and/or rewrite the film to work around Ledger's absence, or whether Ledger's death presents an irresolvable barrier to completion of the $30m film.

This is not the first time an actor's death has prompted a film producer to negotiate with the insurer. Lloyd's of London paid nearly $3m to MGM/United Artists to finish Brainstorm two years after the drowning death of actress Natalie Wood on location; CNA agreed to pay for script revisions, extra shooting, and special effects on The Crow after actor Brandon Lee was shot to death while filming a scene; and a $14.5m payment was made to the producers of Wagons East when actor John Candy died of heart failure. Of these three films, only The Crow saw some success at the box office; the other two were disasters.

As for The Dark Knight, which completed shooting last autumn, as of Tuesday the movie was still scheduled for a July 18 release. But its marketing campaign may have to change. Currently, publicity is built around a series of ghoulish photos of Ledger's Joker. One poster shows him drawing a clown's smile on a mirror with red lipstick and scrawling the words, "Why So Serious?"