He was a super-wealthy Saudi, with lifelong ties to the Intelligence Community, who was the most prominent face of the Muslim Brotherhood in Saudi Arabia (which works to take over the Governments in the region, including Saudi Arabia).
Oh, and he also had ghostwriters publish a few Muslim Brotherhood propaganda pieces in the Washington Post under his name.
His uncle, Adnan Khashoggi, was the billionaire arms dealer who ran the Iran Contra affair.
He was a reporter, a journalist and he pissed off the wrong people. He was as you say, “super wealthy” and now he is dead.
The lesson? Money does not make you kill proof.