There is an interesting video about the attacks 9/11 at Youtube, and attempts to use "witnesses" and the like to prove bombs were planted.
Here it is
When watching this video you should count how many times someone says they heard another person say something about bombs. And how many times people say they heard an explosion, but don't mention anything about a bomb.
Basically, it comes down to this. Nearly all of the quotes in this video are taken out of context, implying they're talking about bombs, when they aren't. If they are talking about bombs, it's nearly always from a third party, and typically that person is never directly mentioned.
Simple fact: news casters are not structural engineers and just because they hear someone say something, does not make it fact when they repeat it.
And an important fact to mention, which they didn't, was that all the buildings had gas tanks for electric generators, in case of power failure. Naturally when those things catch on fire, they explode as well, and create a loud bang.
In the end, "I heard that..." isn't considered evidence of anything, much less science or fact. Just in the same way if someone said "I heard that someone saw a UFO", doesn't really make it true or science.
This video is not science and wouldn't hold up in court as evidence. Sorry, it's bullshot.