Or, they may not have. The L.A. Times spends an article offering speculation but no real scary bits.

The first visit to the U.S. by two of the 9/11 hijackers was to Los Angeles. Their first two weeks here are a mystery. However, they appear to have made acquaintances at the King Fahd mosque in Culver City. A former prayer leader at the mosque (and a Saudi consular official) was expelled last year because of links to terrorists. However, the article doesn't mention any direct connection between them and the prayer leader.

If you were from, say, Morrocco, and you went to the Morroccan district of a city, there's a good chance you could meet up with Morroccans who would take newcomers under their wing. Especially if they were from your part of Morrocco. As others in the article point out, that may have been all that was involved. Speculating...