Most likely they got here on airplanes, just like all the other terrorists we know of. How is this important?
Even if I was to concede that point to be correct, which it isn't... The next attack, and the next incident, and the next smoldering heap after that, and the 1000-year pit of radiation after that will not be the result of people on airplanes, I am more than certain to bet you.
On second thought, forget that bet. I wouldn't want to benefit from such circumstances.