The Department of Homeland Security "red-flags" for further questioning suspicious passengers entering the United States on international flights -- as happened in the case of Raed al-Banna. Here's how it works.

Within 15 minutes after an international flight takes off for the United States, a list of all passengers on board is sent to the National Targeting Center (NTC), part of the Customs and Border Patrol (CBP). The NTC checks the list against terrorist watch lists and analyzes individual passengers for terrorist risk factors. "One factor is national origin, another is travel pattern," explains former CBP Commissioner Robert Bonner.

Those passengers with multiple risk factors are flagged for extra questioning by CBP officers once the plane lands in the United States. Although some details of Raed al-Banna's deportation remain classified, Bonner emphasizes that he definitely qualified for extra scrutiny: "When I say multiple, I don't mean just two -- I mean three, four, five."

"The fact that this guy was pulled aside based on terrorist risk factors is a huge positive for the system," says Janice Kephart, a security specialist who worked with the 9/11 Commission. But what worries Kephart is a problem the 9/11 Commission found throughout the government: information sharing. The risk factors that the NTC sees, and which lead to passengers being questioned further, are not shared with the CBP officers doing the questioning.

"Classified information isn't shared with immigration officers, and so they are put in a precarious position," she said. "They know something is wrong, but they don't know what it is. It's a big problem."

Another problem with the system is the quality of the data used to pull passengers aside. In October 2006, 60 Minutes obtained the federal government's 44,000-name no-fly list and reported that it is both overly broad -- including many common names like Robert Johnson -- and missing the names of some known terrorists, including the 11 suspects in the British airline bombing plot foiled in August 2006.

And the system does not always work; some suspected terrorists are still boarding planes. In May 2005 Hamid Hayat, who was suspected of terrorism by the FBI and whose name was on the no-fly list, got on a plase in Pakistan bound for the United States.

"A mistake was made," said McGregor Scott, the U.S. Attorney who later prosecuted Hayat. "He should have not been allowed to board that plane to return to the United States."

Hayat's plane was diverted after takeoff to Tokyo, where he was pulled off and interviewed by the FBI. The FBI then allowed him back into the United States.

The CBP is working in other ways to improve its terrorist screening procedures and information sharing. It is sending its officers to a special counterterrorism training course where they learn to detect deception and elicit responses from suspicious travelers. As of September 2006, over 5000 CBP officers have received this training.

Also, in response to the August 2006 foiled airline bombing plot in London, airline flying to the United States from the United Kingdom must send their passenger data to the CBP before departure. By 2008, all international flights to the United States will be required to transmit passenger information before takeoff.

This plan may be hampered, however, by disagreements between the United States and the European Union over what passenger data should be shared with American authorities. The two sides came to terms in October 2006, but that agreement will only last until July 2007, when a longer-term deal will have to be negotiated.

This article was a project of the Investigative Journalism for Print and Television Seminar at the University of California at Berkeley, Graduate School of Journalism, taught by Reva and David Logan Distinguished Professor Lowell Bergman and Rob Gunnison under the direction of investigative journalist Marlena Telvick. Reporting by Jeff Kearns, Charlotte Buchen, Jordan deBree, Cathy Bussewitz, Lee Wang and Center for Investigative Reporting intern Taylor Valore. Additional research by Matt Levin, Kate Golden and Joseph De Avila. Additional editing by Alison Pierce of the Center for Investigative Reporting. Special thanks to the Reva and David Logan Foundation and the Gruber Family Foundation.