The hijack bombings appear to me to be an insider job, probably part of a high-level strategy to get the United States more involved in a perpetual religious war in the Middle East.
The parallel I remember best was the simultaneous truck bombings in Lebanon in 1986, when U.S., French and Israeli barracks were hit within a few minutes of each other. The strategic modus operandi was that the U.S. Marines were to be a neutral U.N.-type force. The Marines, including those on guard duty, carried guns without ammunition. Within two days, a truck with six tons of explosives was driven into the building, killing 269 Marines. The bombings of the French and Israeli barracks each resulted in about 20 deaths.
The United States then had a good reason to leave Lebanon and the Middle East. Since that time, Israelis and others have plunged more into daily irregular warfare, and with a lot more terrorism and war. Who really runs the world?