That's the way I understood it during the police press conference. They said Stern was "there" but I took that to mean that he had come with her and was somewhere in the area so to speak, not in the room at the time. They said the bodyguard and a nurse were in the room at the time....no mention of Stern being there.
But I think that was at the very start of the breaking story.
I don't think it's that important if he was there when she died. What's important is where he was when whatever happened to make her dead actually happened.