"The true method of knowledge is experiment."
The Mysterious Eutectic Steel (that looks a heckuva lot like Swiss Cheese):
The above video is by by Jonathan H. Cole, P.E.
The "deep mystery" of the melted steel may be yielding its secrets to investigators not beholden to the federal government.
The severe corrosion of steel beams, intergranular melting, and abundance of sulfur are consistent with the theory of thermite arson.
More building fires for comparison:
Comparison videos of known high-rise steel structure fires of the Parque Central Tower Fire, Mandarin Hotel Fire, Windsor Tower Fire with the fires in the World Trade Center North Tower, South Tower and Building Seven.
Videos of highlighted known controlled demolitions. Both top down and conventional demolitions.