What an asshole! She's trying to dry out, and the bum smuggles drugs to her? The switched cup theory is a valid one. I'm still trying to figure out why Daniel turning 21 would be a reason to off him, though. I have heard about the contents of Anna's will, and I don't recall if there was a clause regarding Stern's control of her assets being nullified if and when Daniel became of age.
I think, based on the info he had approached a PI to help him with his mother, because he thought she was being taken advantage of by HKS and others, that he said something to the effect to Stern on the drive from the airport and Stern offed him to shut him up. Remember, there is the unexplained bruises on Daniel that maybe we'll hear more about at the inquest next week.