According to the medical examiner's office there is no obvious indicators of what killed the "Brokeback Mountain" star, and nothing to contradict initial police reports that the death was not a suicide.
A makeshift memorial of flowers and farewell notes was left outside the downtown Manhattan apartment building where the actor died Tuesday, as fans around the world and family members mourned the death of the Australian star.
Ledger, 28, was found naked and face down on the floor of his rented Soho loft Tuesday with several bottles of prescription drugs nearby.
Police told ABC News that the medications, including sleeping pills and two anti-anxiety drugs, may have played a part in the death which appeared to be accidental.
The death of Ledger stunned his fans and friends. A small display of flowers and candles were set up outside the apartment building along with farewell notes. One message read, "I couldn't find anything bad about you."
The actress Michelle Williams, the mother of Ledger's 2-year-old daughter Matilda, left Sweden where she was filming a new movie yesterday with their daughter to return to New York. Williams, 27, played Ledger's wife in the movie "Brokeback Mountain." The two were engaged, but separated last year.
She received the news at her hotel late last night," said Martin Stromberg, a spokesman for film production company Memfis Film.
Ledger's body was discovered at 3:31 p.m. by a masseuse who arrived at the apartment for an appointment with him, police sources said. The masseuse was let in by a housekeeper, who then knocked on the door of Ledger's bedroom.
When no one answered, the housekeeper and the masseuse opened the bedroom and found the actor unconscious at the foot of the bed, naked and face-down. Police told ABC News they found bottles of Diazepam and Alprazolam, two anti-anxiety drugs, prescribed in Ledger's name.
The housekeeper and masseuse shook Ledger, but he did not respond. They then called the authorities, according to police.
Police added that they did not suspect foul play. Initial reports claimed actress Mary-Kate Olsen owned the apartment Ledger was found in, but police denied that the residence was Olsen's. A police source later said the maid or the housekeeper called Olsen and her security team responded to the apartment on Broome Street.
They said it was not clear who owned the apartment, but Ledger appeared to be a resident.
The superintendent of the building, Tamba Mossa, told ABCNEWS.com that Ledger had "been renting the apartment for about four months" but he didn't know who owned the residence. Mossa added that he was surprised to learn about Ledger's death, saying the actor had always been "very nice" and would often go on walks with his young daughter.
"We are all deeply saddened and shocked by this accident," Ledger's publicity agent said in a statement. "This is an extremely difficult time for his loved ones and we are asking the media to please respect the family's privacy and avoid speculation until the facts are known."
Ledger's family read a statement outside their home in Perth, Australia, Wednesday.
"We, Heath's family, can confirm the very tragic, untimely and accidental passing of our dearly loved son, brother and doting father of Matilda," his father Kim said.
News of Ledger's death hit Hollywood fast.
Two hours after his death was first reported, Nicole Kidman, who hails from Ledger's home country of Australia, released a statement to reporters saying, "What a tragedy. My heart goes out to his family."
"I had such great hope for him," Mel Gibson said in a statement to reporters. Gibson and Ledger worked together in 2000's "The Patriot."
"He was just taking off and to lose his life at such a young age is a tragic loss," he continued. "My thoughts and prayers are with him and his family."
Promising Career Cut Short
Ledger is probably best known for starring in 2005's "Brokeback Mountain," about two cowboys who fall in love. He earned Oscar, Golden Globe and Screen Actors Guild nominations for that role.
Peter Travers, Rolling Stone's film critic, believes "Brokeback" will likely be the movie for which Ledger is remembered.
"He wanted to be an actor, not just a movie star," Travers said. "'Brokeback' was one of the greatest performances of an actor from his generation."
Later this year, Ledger is slated to appear as the Joker in "The Dark Knight," the latest film in the Batman franchise. In a November interview with The New York Times, he revealed how he'd thrown himself into the role, saying, "Last week, I probably slept an average of two hours a night. … I couldn't stop thinking. My body was exhausted, and my mind was still going.''