Did some elaborate conspiracy take place in which CIA black ops snuck in and blew the WTC up? NOT TOO FUCKING LIKELY. However that's not to say there wasn't some level of conspiracy taking place. Why go through all that elaborate planning when they could simply pick up on a planned attack and allow it to go down without interfering? I for one think they knew what was coming and left the gate wide open for it. There's plenty of documentation out there to support the opinion that they simply overlooked what they knew was coming, knowing full well what they could get away with in the wake of the disaster by manipulating the fear of the people.
