Heath Ledger Heath Ledger As news of Heath Ledger's death rocks the showbiz world...

More and more people are questioning why it happened.

The 28-year-old actor was discovered dead in his New York apartment on Tuesday afternoon.

Early police reports suggested the death was drug-related, although results from an autopsy performed on Heath's body yesterday afternoon were inconclusive.

As Heath's ex, Michelle Williams, and their two-year-old daughter, Matilda touched down in New York yesterday, answers were being sought for his sudden and tragic passing.

One of the theories circulating is that sleeping aids that Heath may have taken, including Ambien, could have complicated the effects of pneumonia, which Heath was already suffering from.

Commenting on Heath's alleged use of Ambien, actor Jack Nicholson told the Daily Mirror:

"I warned him (Heath) to stop. I tell people about Ambien. Somebody said 'Take this, it's mild.' I almost drove off a cliff 50 yards from my house."

It has also been reported that Heath was often troubled by insomnia, a condition he made reference to when recently talking about filming The Dark Knight, in which he played the part of the Joker.

"I probably slept an average of two hours a night. My body was exhausted and my mind was still going," Heath told a newspaper.

At the time of his death, Heath had been filming The Imaginarium Of Doctor Parnassus, where he became close to director Terry Gilliam and his wife Maggie.

Yesterday, Maggie also searched for reasons over Heath's passing, saying:

"He was on prescription drugs because he was dealing with tragedy. It was not being with his daughter. It was very, very hard for him. It's a tragedy for everybody who knew him."

However, she rejected claims that he may have taken his own life. Referring to a dinner she and her husband enjoyed with Heath in London a week ago, Maggie said of the actor:

"He was on great form, sparkling and really relaxed. He was speaking about Matilda."

In a moving account, movie director Shekhar Kapur, a close friend of Heath's, also described how he was one of the last people to have spoken to Heath.

"I last spoke to him the night before he died. He said he could not see me that night but really wanted to meet me the next day. He made me promise I would call him in the morning and wake him. I tried but didn't get any response."