Jones was energized in November when he and others received a response from the national lab charged by Congress to determine why and how the towers collapsed. The letter contained the following phrase: "We are unable to provide a full explanation of the total collapse." "That," Jones said, "really was progress. It made me believe we could talk with them." It is striking. After producing a 10,000-page report, the National Institute of Standards and Technology can't explain the collapse. And on its Web site, NIST clearly states that nowhere in its report did it say that steel in the Twin Towers melted due to fires. In fact, the fires reached only 1,000 degrees Celsius. Steel melts at 1,500 degrees Celsius.