Re: "Is every single fact known about the entire chain of events that dark and chilling day?"
Nobody knows every single fact about anything whatsoever.
What we do know is sufficient to conclude that:
1. The 09/11/2001 attacks were planned by Al Qaeda and carried out by its members.
2. The various Federal agencies had their heads up their asses before, during, and after.
Since #2 is standard operating procedure, it should spark no suspicion whatsoever.