Just my two cents - I suppose some evidence of terrorism may turn up, but as it stands now it looks like accidental origin - possibly of electrical origin. The news reported that some people heard a loud bang or explosion just before they smelled smoke. That could have been a transformer or some other sort of electrical equipment, or it could have been a panel shorting out. I would be interested to know if there was an equipment/utility room on 29.
Neither thermite nor gasoline would start as a slow smoldering fire and spread at this relatively slow rate. You almost always find multiple origin points in "incendiary origin" (which is what "arson" is called in the trade), and it usually burns very hot from the beginning. I would have expected a much bigger "flash" to start with if this were incendiary.
I'm sure you are right.
bttt