Okay, so to respond to Ion and others as to why I think WTC7 collapsed in what looked like a controlled demolition. Of course I am certainly not an expert and I am just expressing my opinion.
Let's start off with a simple thought experiment and my numbers are just hypothetical for illustrative purposes. Imagine a 30-story concrete structure that's just a 10 x 10 matrix of non-reinforced concrete pillars with normal strength horizontal connections for each "floor." It looks like a tall thin concrete tower. Suppose that each concrete pillar can support the weight of 10,000 tons. Suppose that at 30 stories high, each pillar is supporting the weight of 9,800 tons.
Don't forget, that we are dealing with pure concrete, no metal reinforcing bars inside the pillars. So what would happen if you took out let's say four of the pillars in one section with cannon fire (or whatever). What would happen? The intact pillars closest to the four destroyed pillars would then have more than a 10,000 ton load and be overloaded and therefore they would explode. This would quickly set off a cascade chain reaction and before you knew it, all 96 remaining pillars would explode because they were overloaded. It might only take 30 seconds.
Meanwhile, when this happened, the 30 story concrete structure would still be standing more or less straight up, because it's so huge and has massive inertia to overcome. In fact, you can imagine that it's center of gravity would still be within the square perimeter of the base. So yes it can fall over eventually, but it takes time because it's so huge and heavy and has a massive moment of inertia.
So think of that model in the context of WTC7. The context is that "all of the materials cost has been sucked out of modern buildings." That means the main support pillars were as thin as the computer modeling and building codes would allow. In other words, a modern skyscraper can be viewed as a structure that is "just strong enough to remain standing and no more," because the architects and the builders try to reduce cost as much as possible, and the way to do that is to reduce your materials cost, all the way down to how much metal you use in your main vertical support pillars.
My pet theory was that when WTC1 and WTC2 fell, they caused two very localized intense earthquakes. Because of the huge momentum of the WTC7 building, in effect many of the main vertical support pillars were somewhat damaged because of the jarring. The ground moved but the building refused to move, so the "ankles" of the vertical support pillars were damaged. Since the structural integrity of the vertical support pillars was compromised, they slowly continued to bend and deform over the period of seven hours right at the base of the building.
Eventually one of the damaged and deformed "ankles" snapped, and then a few others in the immediate vicinity snapped, and then before you knew it they all failed. At that point the building was still standing straight up with it's center of gravity within the outer perimeter. But of course all of the vertical support members became spaghetti curlicues and the building went down.
That was my initial theory.
In looking at the NIST clip, I was a bit surprised that they reported that the fire inside the building was much larger than I think most people thought, up to 10 stories in total vertical displacement. So with the heat buildup, eventually a few of the interior vertical columns failed and the same process took place as described above. There was a cascade failure in the inner rectangle of vertical columns after only a few of them failed because all of the extra strength had been sucked out of the building design to reduce cost. Once the inner rectangle of vertical columns failed then the outer main support wall columns then failed for the very same reason, they were all overloaded at roughly the same time and then the outer part of the building went down.
In thinking about the outer and inner rectangle of support columns (okay the outer "rectangle" was actually a trapezoid) it makes sense that the inner rectangle of columns was probably significantly weaker than the outer rectangle by design. My guess for that reason is that the inner rectangle was much less stressed due to wind forces as compared to the outer rectangle. Since the designers of the inner rectangle did not have to worry that much about compression stress due to wind pressure, they really went on the cheap when it came to the strength of the inner rectangle.
So you combine a weak inner rectangle of support columns with a fire that burns for hours and hours with no sprinkler system working and the building came down.
I haven't read any reports, I am just thinking about my original idea and watching the NIST clip for the first time a few days ago and telling you what I think. You basically had a "perfect storm" for WTC7 and the building came down.