Didn't Really Observe This Before

In this sequence showing the WTC South tower collapse, the top thirty stories almost completely collapse above the break point before the remaining lower, essentially unaffected, 70 stories of building starts collapsing.

I've never been completely convinced that there was controlled demolition of the WTC towers-- even though the physical appearance of the collapse is very similar to controlled demolition.

But the fact that this top chunk of the tower-- which was most affected by the fire-- starts caving in first, as shown in the sequence, this strongly suggests to me there is some type of sequential floor "pancaking" effect going on. Which means the collapse may have had nothing to do with explosives.

Note, the little squibs of smoke, that are highlighted by the author of the page, coming out below the breakpoint are hardly indicative of explosives.

The other thing arguing against explosives is that it is rather unlikely that buildings where thousands of people work could be wired for controlled demolition without people noticing.

So, I am leaning away from controlled demolition of the WTC at the moment, though still not completely sure. Certainly, I find it conceivable that there was something unusual about the structural design of the WTC towers 1 and 2 that made them susceptible to a pancaking type of collapse following a bullseye hit by a large plane and severe fires.