The FEMA Performance Study Group was the first formal investigation of the collapse of the World Trade Center Buildings. From the FEMA Report, Chapter 5:
"According to the account of a firefighter who walked the 9th floor along the south side following the collapse of WTC 1, the only damage to the 9th floor facade occurred at the southwest corner."(emphasis added)
Years later, after independent investigators were focusing on the WTC 7 collapse, the NIST released the photo below as photographic proof there was significant structural damage to WTC 7. Since there was only one photo released, I thought that was odd.
Please note that the damage to the southwest corner in the NIST released photo above is not consistent with the damage in the photo below.
Note the two floors with smoke damage on the southwest corner, floors 29 and 30, in the photo above. Count down 15 floors below foor 29. That corner is missing in the NIST photo submitted as the proof there was significant structural damage to WTC 7 as a result of the collapse of the North Tower.