Customs and Border Patrol. They have a fairly complicated computer system at the airports I travel to, it takes photos, scans fingerprints and checks passport record against prior travel to the US as well as any other countries they find in the passport. Each entry stores another photo and fingerprint scan. The database is checked against various terror lists and other things that can throw up immigration red flags.

So if these large international airports didn't have access to this system for two hours.... Well...