You won't find that out by studying the twin towers as they didn't collapse straight down. The tops tilted a good few degrees before they fell onto the lower floors causing the whole lot to drop down within a smallish area.
Once there was enough weight to collapse the undamaged floors the whole thing was contained inside the tube formed by the outer frame as the floor trusses pulled the sides in. Thus it is very likely that the bottom of the building will collapse straight down the tube. If you look at the videos you can see each floor drop onto the lower ones and the sides pull in.
It won't make any difference to you of course as you have already decided what happened and will ignore the truth.
What gets me is how many people in a burning building continued to work. The first rule in the UK is to get out of a burning building and this cut the death toll amongst the British companies in the trade centre as they just left the building. Its also the reason why British skyscrapers are not as high, you have to be able to exit a burning building by law. There is no way the trade centre towers could have been built in the UK as they were inherently unsafe in a fire.