Generally, their plans are "no witness" plans which would lead me to believe that ONE of the 9-11 hijackers brought the stuff in.
The targets GUARANTEED that it would make the news and give the enemy "let's see what the USA will do" insight.
The first hit on the Towers GUARANTEED it would make the news.
Every year we enroll literally thousands of foreigners in our colleges and universities. They are taught the same stuff right along with us.
They have the backing of rich families or state sponsors and can get extra tutoring and stay through to the PhD. level and beyond. Then we turn around and hire them as employees, set them up in state of the art labs.