A federal officer was watching passengers at Sacramento International Airport on Wednesday when one caught his eye.

A young man in line, unshaven and carrying a backpack, apparently looked suspicious.

The officer was not a typical Transportation Security Administration screener. He was a specially trained Behavior Detection Officer.

BDOs work in the agency's Screening of Passengers by Observation Techniques program (SPOT) and are trained to study a person's face and body language for hints of his mental state.

They roam all parts of the airport, including curbside.

"Officers are screening travelers for involuntary physical and physiological reactions that people exhibit in response to a fear of being discovered," the TSA says on its website.

The young man at the Sacramento airport apparently displayed something unusual. TSA officers pulled him aside for secondary screening, ran a computer check and discovered he was wanted for an out-of-county probation violation.

Sheriff's deputies arrested him. They told us they don't know what triggered the probation violation.

We tracked the man down. He said he had pleaded no contest six years ago to cocaine possession, and didn't realize he was on probation. Nor does he know what he did to attract TSA attention. "I was acting the way I normally act. I was talking to an older lady. We were laughing," he said.

The question some watchdogs ask: Are arrests like this a success for the TSA's anti-terrorism efforts?

The federal Government Accountability Office has been pushing TSA to do more studies on whether the program really can foil terrorists.

A GAO analysis found that the program prompted 1,000 arrests in a recent four-year period, but none was directly linked by the GAO to terrorism. Most people were arrested for being in the country illegally. Others had outstanding warrants. Some were carrying fraudulent documents or illegal drugs.

The GAO noted a National Academy of Sciences report that suggests a terrorist's mental state may not necessarily translate to nervous- or guilty-appearing behavior. The TSA, though, points to a Florida arrest involving a would-be passenger with bomb-making material in his luggage.

The program recently came under fire when TSA officers in Boston complained colleagues were racially profiling. As a result, the TSA said all behavior detection officers, including those in Sacramento, will undergo refresher courses.

TSA officials say they believe their SPOT program is useful.

"We've done a good job showing security does not begin and end at the checkpoint," spokesman Nico Melendez said. "The bad guys know they have to defeat multiple layers of security."

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