The 911 Commission report had NO mention of the WTC 7 building collapse. So your guess is as good as mine.
No plane hit is, and minimal debris hit it. Again, there is NO OFFICIAL STORY on this, so believing it was something other than fire doesn't make you a conspiracy theorist.
Here it is falling in under 7 seconds - from building to dust and molten metal:
We know that the BBC reported it fell, while it was clearly visible in the background:
We see how tall it is - 500+ feet here - along with the 2 localized fires which led to its collapse, according to som:
Probably the best view of it - from the rear - shows the immense size, and speed it destructed, and the conversion from concrete/steel to dust in some explosive event:
http://video.google.com/videoplay?docid=8403741864603265979&q=wtc+7+new&total=870&start=0&num=10&so=0&type=search&plindex=3You can also google video of firefighters telling camerman they were about to bring it down, testimony from NYPF, FDNY, EMS about a 20-second countdown to demolition. it's pretty commonly accepted the building was brought down from a controled demolition.
Problems with that?
---The owner collected $450M and declared there was no controlled demo.
---The building housed fbi and other govt offices - why demolish it with all their stuff inside?
---It takes at least a week to wire a building with explosives. When did they do this and why?
Many call it teh smoking gun of 911 - a building has never converted itself from building to powder/molten steel in 7 seconds like this. There is no official cause, as the 911 commission report won't touch it. And NIST promised a report to explain the collapse. It's been 3 years and it appears they've quietly closed the investigation.
It's an interesting question.