There was never any mention of it being an accident until Jose Baez's opening statement. Casey had ample opportunity to tell law enforcement during her initial interview with police that it was an accident. The officer gave her every wiggle room/opportunity to say so. She never did. Also, during one of the released taped conversations from jail of her with her parents, her mother said the word was going around that it was an accident, and Casey's reply to her mother was "surprise, surprise." She said it rather sarcastically, as if to say, no way. She already had the kidnapping by the nanny accusation out there and intended to stick with it through thick and thin.
Never at all was there any thought or spoken of that it was an "accident." So, you've got to ask yourself, just like Jeff Ashton, the lead prosecutor asked, "who makes an accident look like a murder?"