Plain and simple, shaped charges directly on the affected beams is the ONLY plausible explanation. The fact that this is steadfastly denied in the face of physics implies a much different scenario actually went down that day than they are ever going to admit.
For me the most interesting photos were those from immediately after the explosion in which the building had colapsed, but trees across the street still had all or most of their leaves intact. I don't know where the force of the blast that destroyed the building came from, but it wasn't within the radius of that truck to those trees.
Look just forward of the crane, at the edge/lip of the building damage:
Out of focus, but look at the background behind the fireman:
Tree at the edge of the parking lot and a shrub in the foreground between the street lamp posts...with debris blown OUTWARD from the building's interior.