and as to why it doesn't show up in the secutiry camera video, lets do some math....
The plane was probably doing around 600 MPH.
600 x 5280 = 3,168,000 feet per hour / 60 = 52,800 feet per minute/ 60 = 880 feet per second.
A 757 is either 155 or 178 feet long depending on the type, I don't know which it was so lets assume the longer one.
Also I don't know how wide the field of view is so lets assume it was one plane length.
With these assumptions from the time the nose of the plane appeared until it disappeared into the building would be 356 feet of travel and would have happened in about 0.4 seconds.
Since security cameras like that often have pretty slow frame rates I wouldn't expect to see much of the plane.