Although many detectives who took part in a psychological study had dealt with relatives of dead or missing loved ones who were later revealed as the murderers, they had only a 50 per cent chance of predicting when someone was not telling the truth.
The officers often failed because they relied on unfounded myths, such as the widely held view that avoiding eye contact or blushing are indications of dishonesty, the researchers said.
However, Dr Aldert Vrij, a reader in applied social psychology at the University of Portsmouth and author of the study, said that there were clues and techniques for flushing out liars that the police could use. The best method of detecting a liar is to establish his or her "base-line behaviour", Dr Vrij said.
"There are no typical deception behaviours which people use. The best method is to accuse a suspect of something they are innocent of and observe their behaviour, how much they stammer, the pitch of their voice and the way they move their hands," he said. "Then to accuse them of the murder and see if there are any differences."
Another technique that the police should employ is to question a suspect for a long time going over the same line of inquiry.
"They should never accuse a suspect of lying because often the interview is then ended because the accused decides not to speak any more," said Dr Vrij. "The policeman should keep asking hundreds of questions in different ways, asking for more and more details. A liar will find it difficult to continue making up details and to remember what he or she has said."
Despite no set indicators for distinguishing a liar, there are some good clues that have been found to be relevant to dishonesty, Dr Vrij said.
n Liars are more likely to keep their hands still than those who are telling the truth. Research has found that 65 per cent of people who lie have fewer hand movements than normal.
n The pitch of a liar's voice increases when lying, but most people will not be able to hear the difference.
n People who are lying tend to stammer and hesitate more than those who are telling the truth.
n Liars have more structured answers to questions and are more chronological in their details than those telling the truth. They also tend to give less detailed answers.
Dr Vrij presented his findings yesterday at the British Psychological Society's division of forensic psychology conference at Cambridge University. He told the conference he had shown 52 policeman five video-taped conferences of people appealing for help in finding their relatives or the murderers of their relatives. In every case, it turned out that the relative was the murderer.
He said: "Only half the policemen said the person was lying and lack of eye contact was the most common reason they gave. There is no basis for gaze aversion being related to deception. It is a myth."Reuse content