He seemed eager to learn English in America. So he signed up for a four-month language course in California. Nothing seemed strange about that. When Hani Hanjour didn't show up, the school wasn't alarmed. That happens with foreign students. A year later, he is thought to have piloted American Airlines Flight 77 that plowed into the Pentagon -- one of four terrorist hijackings Sept. 11 that left more than 5,000 people dead in New York, Washington and Pennsylvania.
Most of the 19 hijackers entered the United States legally with the kinds of visas routinely granted each year to millions of foreign tourists, students, workers and business travelers.
Some didn't leave the country when their visas expired. Some may have used phony names. Their success in eluding detection spotlights the plight of immigration officials who are swamped by the flood of visitors and have no real hope of finding violators.
The ease with which the hijackers exploited the system has prompted calls for tighter immigration laws, a moratorium on new foreign students and a narrowing of America's open door.
"The terrorist attacks reveal to the whole world how weak our immigration system is and how lax the enforcement of immigration law has been," said U.S. Rep. Lamar Smith, a Texas Republican and co-author of a 1996 wide-ranging immigration reform law.