The prosecutor is being quoted as being ‘100% sure she was murdered’ - no ambiguity in that statement. And would clear up any of that speculation you point out.
I think the speculation is around what the prosecutor has said. Is he being constantly misquoted or mistranslated day after day?
The point of saying anything in a press conference is to convey information concisely, especially if he is seeking help. You speak to one media outlet who represent all media, you get various media outlets to elect a chief spokesperson who can ask questions on behalf of the whole press. You hand out a statement, which can't be 'disseminated' into a million versions. They could miss out on crucial information, because the public is confused.