There's also video of the outer walls buckling inward as the support beams give way and the entire structure begins to collapse downward from the middle, beginning the 'pancaking' process.

I would still say that fire brought it down though, by burning away walls and other supporting structures, putting too much pressure on the primary supports. The heat also weakened the supports (heated metal isn't as structurally sound as unheated metal, whether it melts or not). Or to rephrase: without the fire, I don't think the collapse would have occurred.