I heard a report that he had pneumonia at the time, and if he had a fever like others I've seen with pneumonia, I can definitely see where this could be an accidental death by drugs, either mixing the wrong ones or not realizing how many he was taking...
Very sad.
I've seen a couple scenes with him as Joker in The Dark Knight, and he was amazing! He was really just coming into his own as an actor, expanding his roles and his body of work. He had so much talent and potential and I truly feel that we, the audience, are must less for having lost him so young.
Very sad.