How about this for validity, you guys can argue all that you want about the towers falling because of weakened steel, thats plausible. Show me the engines of the plane that hit the pentagon please. No matter which way you slice it, jet fuel does not burn hot enough to melt titanium engines. It just wont happen, no matter which way you slice it. So where are they? Did the aliens take them as souvenirs? We'll never know, because thats the way any good conspiracy works.