I saw a program on Discovery channel I think, anyway it showed the test results and opinions of several structural engineers and other skyscraper experts. They had two basic theories of why the buildings collapsed. There used to be a coating of some type on some of the supports that was different than what was usually used on that type of building. They said this change could explain why the steel twisted more than would be expected from a fire.
They also emphasized the point that the burning jet fuel made the fire so much hotter than a regular building fire- really they weren't surprised that the buildings failed. The intense heat caused the steel to warp, twist, strech and what have you until those top floors collapsed- the lower floors were not designed for that so wham, down they came.
They used pictures, video from 9/11, charts, graphs, test results and models to show how it most likely happened; NO ONE on that program in any way suggested demolition or other type of funny business.
Of course they did not have any Department of Labor economists give their opinion- so it could have all been BS. LOL
Dum Administration....never mind.