The link above is a capture of European broadcast video of the WTC-2 collapse, with the north tower in the foreground but shot from a little east of north so you can see quite a bit of the south tower. At the start of the collapse the south tower begins to lean to the south, away from us in this view, so there should be no significant compression (and possibly some traction, if the core has any resistance) on the side closest to us. This means that there is no way from the action of gravity to generate the high pressures it would take to pulverize and eject material in the manner seen. Instead of the kind of slow start we would expect near the beginning of a gravitational collapse we see high speed “demolition waves” coming directly toward us, with another set shooting out to the left, from the east side of the building. These are exactly the sort of confluent rows of small explosions that are so characteristic of a controlled demolition, and can be seen emerging in flat rings extending all the way around the tower and propagating rapidly downward.