It's said the Crown Prince MBS was outraged because Jamal Khashoggi funded Saudi dissidents. He also funded the purchase of international phone sim card for safe communication between Saudi dissidents.
It's alleged the CIA favored Prince Muhammad bin Nayef as the next Saudi King, as he was the Crown Prince before Crown Prince MBS “convinced” Prince Muhammad bin Nayef to abdicate as Crown Prince.
It's also claimed the CIA were pissed-off and done their utmost to expose and tarnish Crown Prince MBS. The Crown Prince MBS has a long list of failures; the Yemen war, torture of Lebanon’s Prime Minister, the conflict with Qatar, human rights violations, and then the death of Khashoggi.
The CIA is allegedly working behind the scenes to usurp Crown Prince MBS.
The US feel Crown Prince MBS has come too close for comfort to Russia and China, as there have been arms deals with Russia (S-400), and China has expressed interest in investing substantial sums of money into Aramco.
Saudi Arabia, and the US signed a 1951 Mutual Defense Assistance Agreement, ensuring the US will come to their rescue if ever attacked.
However, it's doubtful the US will send soldiers to save Crown Prince MBS if there is an uprising within Saudi Arabia. Some say Saudi Arabia has become a huge liability and the 1951 Mutual Defense Assistance Agreement is not worth the paper it is written on.