The east side is on the left, not visible in this photo.
This is the earliest moments is the collapse. We see failure along floor 98 (97?) on the NE corner (red arrow).
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Photo archive of debris in the area east of WTC 1 here
Dropping of the Upper Section
Please note the dark spot centered in the red circle. We will see it is the top of a perimeter sheet.
The top of this perimeter sheet seems to have been ejected quite rapidly from floor 98. Notice how far it has been displaced from the building at this time.
The video clip linked below demonstrate how quickly the top portion shot away from the building.
Both the BBC and the Sauret clips capture the violent early movement of this dark mark well.
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