The thing is, we can wonder all we like. But a criminal investigation cannot be based on "wondering". They have to do things in a certain way, and avoid any of the kind of assumptions we're completely at liberty to make.
This, I think, is a good example of why the tendency of (particularly) the press to regard someone under investigation as almost tried, convicted and hanged, even if they can't actually say that, is a problem. It's completely right that someone who has killed (or just seriously injured) someone else needs to be the subject of an investigation to determine how that came about. One hopes that the police are able to do these things with a degree of sensitivity, but at the same time it really does have to be done.
It's the same with sudden deaths due to other causes (including suicide). Those close to the deceased often find the police investigation, short as it often is, into the death hugely traumatic and upsetting, but there really isn't any way around it - if someone dies suddenly and unexpectedly, it's not for the police to say "oh, look, it must be suicide/heart attack/etc, let's not bother", because people do get murdered and have it made to look like suicide, so to do that would be to make it that much easier to kill someone just by making it look like something else. Personally, I'd not be all that happy with that idea.