If that was your point Clint then they would still have a list of where people said the were going to stay which would be compared to a list of who was actually staying there.

Combine that to finger prints and photographs. If "tourist" X isn't where he says he is going to be staying and doesn't turn up at any other hotel, guest house, whatever, do the rounds of hospitals (he may have been taken ill, or involved in an accident). Do the rounds of vehicle rental agencies just in case he has rented an RV, you still stand a good chance of tracing who you want to find, even if the explanation is totally innocuous. The one you cannot trace, you have a recent photograph of and index finger prints, plus the knowledge that he is probably getting assistance from someone already "in-place".

If you are already at a high alert state, law enforcement and the general public should be more aware. Kevin has always contended that to mount terrorist operations requires little in terms of finance, training, reconnaissance, resources and support. I have always disagreed with that. The measures recently introduced make it more difficult for terrorists based abroad to enter the US and carry-out attacks.