We don’t know who killed Khashoggi. Or why. It was done in such a way as to point a finger at the Saudi government; but there are ways of getting rid of someone that don’t point a finger back at yourself.
It’s byzantine in its complexity, and we shouldn’t base policy on a puzzle.
Khashoggi was a friend of Osama and a staunch supporter of the Muslim Brotherhood, had repeatedly urged the MBL to overthrow the Saudi Royals.
The Saudi Royals got tired of his stuff and did what people in that part of the world usually do ... they got rid of him at the first opportunity - it does not matter to them how, just that a thorn in their sides was removed. Better some bad publicity than an actualized movement to overthrow them.
It is not at all complex, but rather straight forward for what happens in parts of the world where human life has no value.