Looking for signs of stress, fear and deception" among the hundreds of passengers shuffling past him at Orlando International Airport one day last month, security screener Edgar Medina immediately focused on four casually dressed men trying to catch a flight to Minneapolis. One of the men, in particular, was giving obvious signs of trying to hide something, Medina said. After obtaining the passengers' ID cards and boarding passes, the Transportation Security Administration officer quickly determined the men were illegal immigrants traveling with fake Florida driver's licenses. They were detained. The otherwise mundane arrests Aug. 13 illustrated an increasingly popular tactic in the government's effort to fight terrorism: detecting lawbreakers or potential terrorists by their behavior. The TSA has embraced the strategy, training 600 of its screeners ... in detection techniques. The TSA's teams are the most publicly acknowledged effort by the government or the private sector to come up with strategies and technology to detect lawbreakers or terrorists before they commit a crime. Other technologies under development or being deployed include machines that detect stress in voices and software that scans video images to match the faces of passengers with those of known terrorists. The government is testing other technology that can see through clothing with ... electromagnetic waves. TSA's growing reliance on detecting behavior and the close study of passengers' expressions concerns civil liberties groups and members of Congress. "The problem is behavioral characteristics will be found where you look for them," said John Reinstein, legal director of the American Civil Liberties Union of Massachusetts.

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