"A measure of abnormal long put volume was also examined and seen to be at abnormally high levels in the days leading up to the attacks. Consequently, the paper concludes that there is evidence of unusual option market activity in the days leading up to September 11 that is consistent with investors trading on advance knowledge of the attacks".[67] —Allen M. Poteshman, The Journal of Business
I've kind of swung back and forth on the specifics because there's some truly ludicrous theories out there, ie planes didn't hit the towers, it was missiles and the Mandela Effect is just that strong plus every video made of the day was seized and altered by Donald Rumsfeld. But since around 2007 or so I've been fairly adamant that at best, Cheney, Rummie, and a select few others all knew that an attack was imminent and did nothing to prevent it (or helped out in a few key moments) to at worst, controlled demolition brought down the towers with nano thermite, the Pentagon was hit with a CIA plane loaded with some explosives, and flight 93 was shot out of the sky. Kind of doesn't matter, since either way you have complicity.
But we all know that tower 7 didn't just decide to sit down after a long day of being on fire.