Elaboration:

Threat profiling involves many aspects such as country of origin, ethnicity, religion, traveling habits/patterns, etc. If you meet a certain profile, one should never be allowed into the U.S. and certainly the privilege of traveling by air should never be granted. Hell, Atta had overstayed his visa in 2000 and but was allowed back into the country again and he was also placed on an FBI terrorist watchlist in August of 2001.

As for the Lindh nutcase, he converted to Islam when he was 16 and in 1998 he began a 1 year "holiday" in Yemen, hobnobbing with fellow Isalmic radicals. He was allowed to return (under my proposed system he would not have been allowed to enter the U.S.) to the U.S. after this year and studied at a Mosque in San Francisco and finally left the Superpower in 2000 to join up with UBL.

Last but not least due to the WMD plot of this Koran reader, Padilla was arrested on May 8, 2002 at Chicago's O'Hare International Airport after arriving from Pakistan. Yes, threat profiling does work.

Just read chapter 7 of the 9/11 commission report that details the arrivals of these Islamists and it becomes evident that threat profiling would be an extremely effective solution to prevent terrorist acts.