Justification for the Saudi purge would not necessarily have to have been proof that they attempted POTUS assassination; what if JK went over there and said 'we have the proof you were involved in 911." Followed up with, "Unless you purge Saudi Arabia, implement more friendly domestic policies, actively root out terrorism and the ideologies that create it, we will nuke you into dust because you attacked the USA." And "We'll even let you into the Exchange Markets in NYC."
That all being said, I believe the planefags would know more about what aircraft actually came in to LV that night.