well, that must mean that some of these guys were caught somehow - and they determined their method of entry. or, they broke up a ring of people already inside the country who were facilitating them being brought in, and the method was revealed in that manner.
Joe, do you remember the ring of Mexican immigration officials who were all arrested because they were facilitating the entry of Mid-Easterners and Chinese? It was posted on FR - what? - about 3 months ago.