On my point of view, the best way to reopen the 9/11 investigation is a call to American tourists who went to Prague in April 2001 and see if the Atta-Al Ani meeting had been caught on tape or photograph.
It is possible people have it but never checked.
Atta went to Prague several times between 1999 and 2001.
If you visited Prague during this period...
Sometimes, the best evidence comes from the most unexpected things...