The story of the collapse of the three, not just two, World Trade Center towers is fascinating. Two towers were struck by air planes and the debate has been whether this was sufficient to create the pan-caking collapse effect. But no planes struck the third tower, WTC 7. The official report has it that fire and debris from the other explosions structurally damaged WCT 7, leading to its pan-caking collapse, which looks just like it was imploded. That has long been disputed.
Now there is a structural re-evaluation of the collapse of WCT 7, by the Institute of Northern Engineering, University of Alaska Fairbank. As would be expected the report is complex with engineering considerations. But for our purposes, what is significant is the conclusion: fire did not cause the collapse, and there was a simultaneous collapse of every column in the building. The report did not go onto speculation what did cause the collapse, as this was outside their terms of reference. However, at that point, engineering goes over to politics. The only plausible mechanism for the simultaneous collapse of all columns is that the building must have been imploded, a deliberate explosion. If this is so, who did it, and how does this bear upon the collapse of the other buildings?