This video is was made during the construction of the WTC. In it, one can see how the WTC was constructed. The massive steel core columns were bolted to the bedrock under the WTC buildings, and were thoroughly crossbraced This video even says that the outer shell was designed to transfer some of its load to the core (not the other way around)...
This video has footage of one of the people responsible for the construction of the WTC (I believe he was the project manager), and some quotes from John Skilling, who was the chief structural engineer of the WTC. I had heard him referred to as a designer, but I guess that may not be the best way to refer to him. However, these two people were part of the team that was tasked with realizing the architect's intention for the way the buildings were to be constructed. Both of these people talk about the focus on constructing the buildings in such a way that they would be able to withstand the kind of event that happened on 9/11. The relevant footage is a little more than halfway through. The rest of the video has relevant material as well, and Simple scientific principals guide the approach being taken by the makers of this video...
This paper has a lot of documentation that debunks a lot of the government's version of events, and it also effectively destroys a lot of the assertions made in the paper catspaw linked in this thread, including the alleged seismographic evidence...