The man in the cheap brown jacket slumped in line, staring at the ground. His hands were fidgety, reaching repeatedly into his jacket pocket, or patting it from the outside. A momentary look of anguish, just a fraction of a second or so, occasionally flashed across his face: the inner corners of his eyebrows would go up, so that his brows sloped down from the center of his forehead; his cheeks would rise; and the corners of his lips would pull down slightly. He was exhibiting what I call a micro-expression, a sign of an emotion being concealed.
The question was: What was he concealing? And why?
To the behavior-detection officers I was with at Boston's Logan International Airport, his combination of mannerisms - the micro-expression, the slumped posture, the pocket-patting - raised a red flag. They called a state police officer, who asked the man the purpose of his travel. It turned out that he was going to the funeral of his brother, who had died unexpectedly. That was the reason for the bowed head. The frequent chest-patting was to reassure himself that he had his boarding pass. The micro-expression was an attempt to conceal his grief.
The man was not a terrorist, just an innocent traveler carrying some extra emotional baggage that day. So why single him out for questioning because of a fleeting expression and a sad-sack posture?
Critics of the controversial new security program I was evaluating - known as SPOT, for Screening Passengers by Observational Techniques - have said that it is an unnecessary invasion of privacy, based on an untested method of observation, that is unlikely to yield much in the way of red-handed terrorists set on blowing up a plane or flying it into a building, but would violate fliers' civil rights.
I disagree. I've participated in four decades' worth of research into deception and demeanor, and I know researchers have amassed enough knowledge about how someone who is lying looks and behaves that it would be negligent not to use it in the search for terrorists. Along with luggage checks, radar screening and the rest of our security arsenal, observational techniques can help reduce risks - and potentially prevent another deadly assault like the attacks of Sept. 11, 2001.
Much has been said about the Sept. 11 hijackers' unusual behavior in the days before they boarded their ill-fated flights. Several were repeatedly questioned, but no one recognized their lies. An airport screener later said he had been suspicious of one because of his strange demeanor that day. But the screener had no training that would have given him the confidence to act on his suspicions.
The hijackers' lies - to visa interviewers and airport check-in workers - succeeded largely because airport personnel weren't taught how to spot liars. The people who might have saved the lives of many Americans were needlessly handicapped.
Imagine if that screener had been taught to discern the signs of deception in a person's facial expressions, voice, body language and gestures, making him confident enough to report the hijacker's behavior. SPOT, which the Transportation Security Administration introduced this year at 14 U.S. airports, is the first attempt at using observational techniques as part of our security approach, and it is promising. Preliminary findings show that the overwhelming number of those detained for further investigation were intending to commit or had committed some kind of wrongdoing: They were wanted criminals, drug smugglers, money smugglers, illegal immigrants - and, yes, a few were suspected terrorists.
SPOT's officers, working in pairs, stand to the side, scanning passengers at a security checkpoint for signs of any behaviors on the officers' checklist, such as repeated patting of the chest - which might mean that a bomb is strapped too tightly under a person's jacket - or a micro-expression.
Items on the SPOT checklist are culled from law enforcement experience and research on deception and demeanor. What about your face, voice and body betrays the fact that you're lying? I've studied this question for nearly 40 years, since I began researching it in the 1970s with Maureen O'Sullivan, of the University of San Francisco, and later with Mark Frank, of the State University of New York at Buffalo.
We recorded interviews set up in such a way that we knew when a person was lying. Afterward, we replayed the videotapes repeatedly in slow motion to identify the expressions and behaviors that distinguish lying from truth-telling. We spent hours identifying the precise moment-to-moment movements of the facial muscles based on my Facial Action Coding System (FACS) - a catalog of every conceivable facial expression that I created and published in 1978 - to get comprehensive evidence of the kinds of facial looks that accompany spoken lies. Once such expressions are identified, people can be quickly trained to recognize them as they occur.
We also looked at the behavioral signs that accompany the act of thinking up an answer on the spot (e.g., an increase in pauses) and signs of emotion in the face, voice or gesture that contradict the words being spoken ("The answer is definitely no" accompanied by just a slight nod of the head). The facial expressions we identified allowed us to correctly determine who was lying 70 percent of the time; adding the rest of demeanor pushes accuracy close to 100 percent.
Such tools are indispensable to the future of airport security, and more are coming. Within the next year or two, it will be possible to program surveillance cameras hooked to computers that spit out FACS data to identify anyone whose facial expressions are different from the previous two dozen people in line.
Someday, remote surveillance devices may identify anyone whose blood pressure and heart rate are much higher than those of the previous two dozen people. While this will provide an important new way of knowing that something is amiss, it does open a Pandora's box. Legislation to protect privacy and prevent misuse of such a technique should be enacted now.
Meanwhile, short-term research on several questions - whether SPOT misses people whose behaviors are on its checklist; whether other behaviors should be included on the list; and whether additional training would increase observers' accuracy - could help improve the program. Civil libertarians have raised the expected concerns about using observational techniques at airports: that SPOT spots more than just terrorists; that minorities, who fear discrimination and might act more nervous than others, may be unfairly singled out; that most of the people identified are innocent.
But the day I spent at Logan confirmed for me that SPOT violates no one's civil rights. Few people were identified. Nearly always, the answers to initial questions made further investigation unnecessary and no record was made.
Observational techniques are not a substitute for all the other techniques we now use to catch would-be terrorists. But they add another layer to transportation security. They are now being used at fewer than one in 10 major U.S. airports. We need to use them everywhere.
Paul Ekman is a former professor at the University of California at San Francisco and an adviser to the Transportation Security Administration. He wrote this article for The Washington Post.