I've seen this photo before, I'm posting the link to it for those of you who never have.
That's a 45 degree cut from a thermate charge. I've seen them in the military used in a variety of contexts.
There is only one way on earth that this beam could look like that. It's not a structural collapse from fire. That beam was surgically cut with a thermate charge, as were all the other beams in that "collapse." Those charges were all set during the building-wide "power-down" a few days beforehand when the building was emptied except for the same security team in charge of the cleanup afterwards, when they shipped off all of these beams to be melted down immediately.