Opinion — no citations yet
Marked sensitive
The author has not said this one is safe to show without warning.
Every note starts marked, so this usually means nobody has cleared it rather than that anything is wrong.
It says nothing about whether the claim is true.
Determine what specific warnings (e.g., PDBs, foreign intelligence tips) existed before the attacks, who received them, and whether failures to act reflect negligence, bureaucratic breakdown, or something more deliberate.