There are hundreds of credible people who dismiss the official story
A common tactic used to debunk questions surrounding the official 9/11 story is to claim that if there was inside involvement in the plot, whistleblowers would have gone public and exposed the conspiracy.
The claim assumes that conspiracies cannot be kept covered up, a fallacy disproved by the Manhattan Project. The development of the nuclear bomb was kept hidden for years before its announcement, despite the fact that thousands of individuals from all kinds of different disciplines worked on the project.
This proves that top secret, highly sensitive operations can be covered-up. In comparison to the Manhattan Project, 9/11 was miniscule in its reach, and only required the foreknowledge of dozens, not thousands of people, to be successfully carried out.
In addition, there have been numerous whistleblowers who have gone public and used the knowledge from their respective fields to dismiss the official 9/11 story.