"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
EXACTLY this isnt a solid concrete bunker we are talking about, we are talking about just enough concrete to hold up a bunch of steel glass and paper in the air.