According to my theory; the government did not blow up the buildings directly, but the highest levels of power (ie. Bush and company), were aware of what was about to happen. More likely, MOSSAD was tapped to plant the bombs. Insofar that the U.S.A. is little more than a puppet of Israeli policy (AIPAC anyone?), yes it is a global Zionist conspiracy (to differentiate from your typical Jewish person). Al-Qaeda was probably involved in the plane hijacking, unwitting puppets of the plan (remember, the CIA was working with bin Laden back in the 80's, and they were instrumental in helping Al-Qaeda cast down Gaddafi in Libya). The planes did hit the buildings, but the buildings would not have collapsed from plane impacts alone. The planes were used to a) implicate Al-Qaeda in order to justify conquests in the Middle East (see the Pentagon's report "Project for the New American Century", published in 2000, that states the U.S. can only protect its interests in the Mideast with aggressive action, but such action would not be justified "short of a new Pearl Harbor" [!!!]). Planes were used instead of 18-wheelers in order to justify upping airport security and tightening border control. So many people were allowed to evacuate because the people weren't the target, it was simply the enormity of the act, a "new Pearl Harbor" in effect, that was required. The explosives were not detonated right away because they wanted their story to be at least semi-believable (at least, to the unenlightened masses).