After the destruction of WTC1, this stairwell in the core of the building remained-- three to four stories higher than the rest of the rubble pile:
Now remember the "spire" of WTC1 that remained for a few seconds during the destruction of the tower?
It was a good 70 stories high, and was part of the WTC1 core:
The spire didn't topple over, but fell more-or-less STRAIGHT DOWN:
IF THE SPIRE MERELY COLLAPSED, FALLING STRAIGHT DOWN, THE HEAVY CORE COLUMNS SHOULD HAVE OBLITERATED THE STAIRWELL AT THE BASE OF THE CORE!
Rather-- the stairwell WOULD survive if the spire was blown with bombs at the base-- a few stories above the stairwell. In this way, the higher spire columns could fall to the side as the base was blasted out. Perhaps several bombs along the base of the core were used to create this result. But it seems clear that a collapse of the spire could not result in this intact stairwell. It also seems likely that this nuclear blasting along the core/spire would account for all the missing WTC1 core columns!