I have an old friend of mine that was working on a high rise in Jersey City when both aircraft hit the trade center(s). He's the forman for concrete work on that building. He is also a pilot.
He told me that he watched both aircraft hit the buildings. He couldn't believe it. Distance was a little over a mile.
I asked him about your comments on "conspiracy". He laughed and told me that with that much heat on the main steel structures a collapse straight down was nothing surprising. The heat weakened the girders and when they gave way the upper portion of the building became a pile driver to collapse the lower structure. The lower steel girders were NEVER designed to absorb a shock like that. It was much better to have the building collapse than "fall over" and take many buildings and people with it.
I have no doubt he's correct, IMHO...
By the way I'm a recently retired 747-400 Captain and nothing that I've seen or read about 9/11 makes me think anything other than what has been reported. FWIW