Very good question, very well put.
Not "who flew the planes which destroyed the twin towers" - that would presume too much. But instead, merely, "who"?
- As a number of recordings made on that day show without a doubt, it was not caused by the planes crashing into the towers, but rather a meticulously planned demolition. To answer the question "Who"? Obviously a well-organized group of people with the money and resources to plan something this big, keep it hush, and with both the motive and the incentive to do this. The U.S. Government.