The house of Saud admits he was killed by their guys. But If a bunch of FBI agents killed someone, would you say Trump was a murderer? Of course not!... until we conducted an investigation finding he had authorized it.
Like I said, some unauthorized action in the chain of command is entirely possible.
Instead of Trump, lets talk Obama. He and Valjar were behind a lot of illegal, nasty stuff. But sometimes people in his administration acted on their own, without direct command.
It could have happened here. I think that we agree on that possibility.
My big wonder, as I said before, is why do it this way? A simple professional anonymous hit would get him out of the way, if that was all that was desired. Somebody really hated Khashoggi.