There is not one angle which tells the complete story. If we had a direct southern view and a direct east view it would be clearer, but here for starters. The perimeter wall collapse began as a shift to the east, illustrated in this screen grab:
In actuality, it was more of a twist than a shift. The left (east) part of the building is actually folding towards the camera. It began this move PRIOR to descent, which rules out having it's underpinnings suddenly cut out from underneath it. Lower support was folding.
The west, or right part of the building was falling away from the camera, evidenced by my avatar.
The perimeter walls could not have folded vertically in this manner had they been intact. This movement is in accord with the top to bottom gash on the south face.
Additionally, debris fell across Barclay Street to the north, creating so much damage to Fiterman Hall, it had to be torn down. The west portion of 7 fell to the south, across the street and into 6WTC, again, evidenced by my avatar.
Undo what Wilson did