were the only muslim people in that line. >> reporter: u.s. customs and border protection told cnn, quote, the religious faith or spiritual belief of international traveler are not determining factors. for flights in or out of the united states, passenger security checks happen long before travelers get to the airport. even before the airline accepts payment, names are run against the government's no-fly list. if there's a hit, the sale is denied. for those who've bought a ticket names are continuously checked against other government databases searching for everything from past itineraries to law enforcement, if there's a problem the airlines deny boarding at the airport. but it's not just terrorism. there are other reasons a passenger could be denied boarding, like incomplete documents or health-related issues. now we know some members of this family had dual citizenship in the uk and pakistan, and it's