The only reason I brought up the federal building is because it was damaged and imploded.
Would this be the final report on WTC 7 from NIST?
http://wtc.nist.gov/pubs/WTC%20Part%...se%20Final.pdf
It looks like there were some flaws in the design of the building, and they did a good job explaining the collapse.
From other sources, there are sounds 9 seconds ahead of WTC 7 collapse, if they are explosions or collapsing material, I don't know. I think there are ways to take out a building quietly, but it might take a while and go into the paranoia column.