9/11 still happened with people that didn't appear "normal"

Actually, they did appear normal. USA is a very multinational country, and these guys would not look much different from the rest of the passengers. Especially in international airports of large cities of the Eastern shore where they boarded the planes.

(Mohammed Atta could be an exception. Not by the looks, but by his facial expression. I believe I saw him with a few of his co-conspirators several months before 9/11, and he did stand out.)