The squibs look suspicious to me. The explosions were forceful and directed, there was a lot of particulate being ejected in what were narrow streams, and they all seemed to be centrally localized.
According to cross-sectional diagrams of the floors, the facades of the buildings were 208 feet wide. Am I supposed to believe the path of least resistance for the air contained between each floor wasn't out the sides of the building at the collapse wave itself? The explosions can be seen several floors below the collapse wave. I would think the next-to-least path of resistance would be the elevator shafts. Lets assume it was air that caused the explosions. Regardless of how it flowed downwards we have to believe that the windows near the corners of the building were strong enough to contain this mass of rushing air that may have traveled more than half the length of the facade in order to be narrowly ejected through the apparently much weaker windows in the center. Or, the air pressure was that much greater at those points for some reason.
I find it hard to believe that the strength of the windows could vary this much or that the weak windows would coincidentally be at the center of the facade. On the other hand, what if it did indeed go through the elevator shafts? If the elevator shafts were truncated at various sections of the building, then it might be expected that once the air hit the bottom of the shaft it would shoot out the side in a very forceful and directed manner, producing the explosions that we saw. If the elevator shafts traversed the entire length of the building, then the air pressure explanation doesn't seem feasible to me.
Has anyone analyzed the relative locations of the squibs with the layout of the elevator shafts to see if they correspond to where the shafts are truncated, if at all?