Aren't the physics fairly straightforward? To knock down steel reinforced concrete you need an enormous shockwave - a jet doing several hundred miles an hour should do the trick - and enormous heat - as generated by enough aviation fuel to reach the west cosat for instance - to destroy the tensile strength of the steel rods supporting it. Most of us would not abuse our imagination to think up something as awful as that. We can blame nobody for not forseeing it. I'm staying out of the politics here. My condolonces to al the bereaved.