This is fascinating. I can think of no reason why the US authorities would say it was the impact of an aircraft when it wasn't, and no reason why the missing aircraft could be missing. BUT the security camera shots given by GUEST at this site don't actually show an aircraft, just an explosion. If the commentary wasn't talking about an aircraft, you would not suspect the presence of one in the entire sequence. The questions given at this site are valid - look at these photographs and try and answer them yourselves!
We all saw the damage done to the two towers by the same type of aircraft at the time of impact - where is it here?

Cheers
Ray (a retired scientist who spent his working life answering the same type of question)