Never forget who is who !
"They may have been Saudis, we may never know their nationalities"
Six of the fifteen Saudi hijackers were using fake/stolen IDs from people who are still alive. They may have been Saudis.. We may never know their nationalities.
Something to take into consideration is that Saudi students have been getting US visas since 1950 so its much easier for a Saudi to get a visa than any other nationality in the region.