If the building was believed to be brought down due to intense fuel fire that reached temperatures over the melting point of steel. Yet, it was clear that the temperature couldn't have been that intense and even if it was near that, the building wouldn't have collapsed. The proof for that is many high rise fires and most of them burned for 17+ hours, the twin towers burned for 100 minutes. Most eye witness reports indicate the presence of secondary explosions after the initial impact. Which really indicates that the buildings were brought down by controlled demolition, as the speed of the collapse was 10 seconds, which was exactly the same as free fall speed. Common sense should dictate that when a building collapses upon itself in such circumstances where the upper top portion of the building was burning and the lower part remained untouched, the building's collapse time would be delayed due to the resistance from a multitude of floors.
As videos show, the collapse looked too smooth, and the fact that secondary explosions were present (as previously stated) really points to the fact that controlled demolition had taken place. The building had also been designed to withstand SEVERAL hits from a Boeing 707, which is a considerably larger plane with 4 engines instead of 2 engines on the 767's that hit the twin towers, and the towers would withstand speeds of up to 600 miles per hour, whereas the 767's were moving at the speed of 450.