A wmv video of the World Trade Center's Tower 1 is available by clicking here.   It is of the tower, just prior to and during the initial phase of its collapse.  

Note that only a small area of the tower's base is visible through a small separation between two other buildings in the distant foreground. It's what happens at the base of the tower, just before it collapses, that indicates there were explosive charges set off to bring the tower down.

Here's what to consider when viewing the video.
Could explosive charges at the tower's base have caused the smoke, prior to its fall? 

The 911 Commission conveniently ignored the issue.