Some police see through killer's lies.

Murderers brought in for questioning by the police have plenty of reasons to feign innocence. What's worse, according to several studies over the past decade, is that people, including police, are quite likely to be duped by such liars.

But some cops can't be fooled, according to a new study. Shown video-tapes of an interrogation of a murder suspect speaking a language they didn't understand, some British police officers consistently knew when the man was lying and when he was telling the truth. Other officers detected lies and truths about as well as if they had guessed, and some detected lies less often than if they had guessed, report Aldert Vrij and Samantha Mann, both psychologists at the University of Portsmouth in England.

Their study, published in the March-April APPLIED COGNITIVE PSYCHOLOGY, assesses, for the first time, people's ability to size up a highly motivated liar. Earlier deception studies had used people who lied at the behest of experimenters. With little to lose by getting caught, laboratory liars are better able to obscure their falsehoods, Vrij and Mann say.

"[Volunteers] holding popular stereotypical views about deceptive behavior, such as `liars look away' and `liars fidget,' were the worst lie catchers," the researchers observe. The best lie catchers noted that the suspect spoke much more slowly and with more pauses between words during lies.

For their study, Vrij and Mann obtained a videotape of two police officers interviewing a murder suspect. Although the suspect denied knowing and killing the victim, evidence later showed that he was lying. The suspect then confessed in a second videotaped police interview and was convicted of murder.

The researchers selected six segments from the interviews. Three showed the suspect lying about his activities on the day of the murder. The remaining segments featured truthful statements.

Of 65 police officers shown the segments, 18 made no more than one error in detecting lies and truths. Another 36 judged three or four segments correctly, and the remaining 11 identified only one or two segments correctly. Because the words were unrecognizable, they had to detect lies using nonverbal cues and speech intonations.

Individuals use a variety of deceptive tactics in high-stakes situations, remarks psychologist Mark G. Frank of Rutgers--The State University of New Jersey in New Brunswick. In lab studies, some people betray lies through brief changes in facial expression while maintaining a constant speech rate, he says. In contrast, psychopaths give away their lies only through inconsistencies in speech content, in his view.

"This is the first good look at lie detection with a liar in a do-or-die situation," Frank says. "But there's no way to know if [the murder suspect] was a good liar or not."