I agree. The NIST report makes the point that they were 90% empty space, and could easily collapse on themselves. The suspicious points to me include WTC7, the recent purchase by Silverstein, Silverstein's "pull it" remark, molten metal in the bases, and the fact that when they went to remove the gold in the basement, someone had already been there trying to break in!
How could somebody possibly have been digging around in the gold storage area without being noticed?
The amount of gravitational energy unleashed when the Twin Towers fell was on the order of a small nuke. I forget what power-of-ten joules I calculated, but it was pretty darned huge. All that energy all had to get converted to some other form, and an awful lot of it got turned into heat.