I think that you're missing the point. Most of the people in the 9/11 Truth movement are asking for a further investigation. They point out a lot of things about the events (stoked by people who act from self interest) which they want to know more about. Furthermore, you have a second problem in that the movement contains people with ideas that are easy to rebut (space deployed beam weapons) to people with more subtle arguments which require advanced mathematical knowledge to understand. I doubt that the NIST, et.al. will ever have the funding or the inclination to investigate every claim, so this is just going to go on. They don't have to answer any questions, they are just pointing out things which they find fishy and asking for an investigation.