It most likely has something to do with the person having drugs in their possession or in their luggage. As for having an outstanding warrant, they wouldn't know that unless Immigration was alerted when they run the name upon re-entering the country and even then, you better believe it would have to be something very big and probably n a Federal level. Ther are not running an NCIC check at this time to my knowledge. If they are, good, those entered in that system need to be taken off the streets. Parking tickets, or other misdemeanors, no way.