Dallas is far enough north that folks don't automatically assume that foreign looking, non-English speaking, dark skinned folks have just swum the river. Yet, it is close enough that a small fleet of vehicles, 4 door pick up trucks or vans, could pick up teams of other Muslims very near the border where Muslim coyotes left them and bring them north to Dallas.
Cargo in the form of dope, guns, kerrorist materials or quantities of cash could also be carried. A cargo depot could easily be established at one or more of the hundreds of self-storage complexes in the area. So, the FBI got one of the kerrorist cells. How about all the others?
Bingo, you got it!
But what's a "kerrorist"?