As far as the collapse of the three WTC towers in 9/11, the official investigation (and others supporting it) is not convincing. The real question is how can three skyscrapers collapse in a controlled manner the way they did in 9/11? Structural damage; whether caused by fire, impact or debris should not cause the buildings to fully collapse and in such a controlled way. Demolishing a building is a science in its own right and needs experts to do it. If three skyscrapers went down in an almost controlled manner in the same day then I must say we don’t need demolition experts anymore. Why do we need to fill buildings with explosives in order to demolish them? Why don’t we only plant explosives at the top floors and watch the building collapse as the top floors take care of the floors below like the WTC towers?
Structural damage can cause a building to partially collapse; for example at one side. The building should basically collapse gradually. But in 9/11, three buildings, the first: boom .. from top to bottom, the second: boom .. from top to bottom, the third: boom … from top to bottom. No where else this have been seen except in controlled demolition. Buildings tumble on one side, partially collapse, etc. but not fully and very fast.