Isn't it also a serious question how free fall acceleration could occur in a controlled demolition collapse? I am just asking this since most videos of controlled demolitions I have seen are slower than a free fall. This is quite plausible as in the controlled demolition you want to use the potential energy not be 100% converted into kinetic energy (100% conversion is equal to free fall) but use a considerable ratio of the kinetic energy to smash part of the structural elements that support the building. First I would like to emphasize that I understood that not the whole building descended at free fall and also not all of the descend was at free fall acceleration. The measurement of free fall is just verified for some distinct points of the facade, and only for some intermediate time after the start of descend. I hope we can agree on that. I can understand your doubts. But the question is how to verify if they are justified or not. This is not easy. How much time do you think is reasonable for the interior buckling or collapse to progress westward? What would you set as a maximal speed of progression? Maybe you want to have a look at these rack collapses, which IMO collapse quite rapidly: You see in the videos a collapse initiating event, followed by some intermediate transient phase, followed by rapid progression to global collapse. Once the support is lost at a local level, the structure shifts loads to the remaining columns, which can't support these loads and collapse very quickly.