You’re very naive if you think Bush didn’t know the day of the attack who was behind it.
There are only two ways to think about this in that context. One, that Bush knew the day of the attack, because he knew before the attack - and I reject that. Two, Bush had a good idea who was behind the attack (after the attack), primarily because it bore the trademark of bin Laden (lots of people thought this at the time) and because of the intelligence that was given to him after the attack. The documents themselves state that the intelligence agencies didn't consider the Saudis as exporters of terrorism at the time of the 9-11 attack, and thus IMHO it is doubtful that Bush was given definitive intelligence at the time stating that the Saudis were complicit in the attack.
Plus, I don't think of the Saudis as a monolithic entity. I don't trust them in the slightest, but don't think that the entire family is in the business of exporting terrorism. IMHO there are factions within the Saudi family that are more problematic than others, and that the Saudi right hand and left hand don't always play in concert. I also think that the Saudis hold on power in SA is fragile, and that the US government and intelligence agencies don't know sometimes which is the worst scenario - the continuation of the nefarious state of SA, or what would replace it if the Saudi family lost control.