I don't think the 9/11 question stays unanswered forever. It was recorded by many different people. AI will be able to tell us if what happened was possible given the information we're told, and if not, it will be able to tell us how it is possible.

Of course, whoever controls the AI might have an agenda, but there surely comes a day where it's not possible for humans to hide their commands to AI. I doubt that day is in my lifetime, but in 100 years I think it will be resolved.