Quite simple to pull off really, all they had to do was have explosives planted in the base of the towers, and on 9/11 they pretended like 4 planes were being hijacked when really they just rerouted them to Pennsylvania, then flew two military jets into the World Trade Center filled with more explosives and shot down all the witnesses on Flight 93 with an F-15 after blowing up the Pentagon with a cruise missile. It was only the world's most intricate and flawlessly executed plan ever, ever.