I recently read a very interesting book "The Eleventh Day: The Full Story of 9/11 and Osama Bin Laden" by Anthony Summers and Robbyn Swan.
In the book, the authors make a very strong point that, lost in all of the crazy conspiracy theories surrounding 9/11 (W knew about it and let it happen; W planned it, etc.) is the strong and plentiful evidence that members of the Saudi government not only know about the impending attacks but funneled tens of millions of dollars to Al Queda in the years preceding the attack. Also much evidence that this was overlooked/whitewashed by the 9/11 Commission and the U.S government because cheap oil. The very fact that the administrations of W, Obama, and Trump all refused to release information on this matter has only strengthened the claims of whitewash.