the response to any conspiracy theory, including this one, is the famous statement by Benjamin Franklin - "Three people may keep a secret if two of them are dead."
It was true when he said it, and its true now.
Consider the number of people that would need to be involved in something as elaborate as a murder staged to resemble an accident, and then wonder how long it would be before just one, and it only takes one, person blabbed to someone else, and the story got out.
It's simply not possible to stage this, and then have everyone involved stay silent for ever, it would never ever happen.
The answer therefore is what is left - it was an accident.