Witnesses can catch criminals by smell: study

London: Move over, sniffer dogs! People who witness a crime can identify criminals by their smell, according to a new study which found that humans are able to distinguish individuals by their unique body odour.

"Police often use human eye-witnesses, and even ear-witnesses, in lineups but, to date, there have not been any human nose-witnesses," said Mats Olsson from Karolinska Institutet in Sweden. We wanted to see if humans can identify criminals by their body odour," said Olsson.

Dogs have been used to identify criminals through body odour identification in court, but it is commonly thought that the human sense of smell is inferior to that of other mammals.

However, research shows that humans have the ability to distinguish individuals by their unique body odour.

Our olfactory sense is often associated with emotional processing and is directly linked to the areas of the brain associated with emotion and memory; the hippocampus and the amygdala, researchers said.

To find out more about human odour memory following stressful events, researchers investigated how well we identify body odour in a forensic setup.

In their first study, participants watched video clips of people committing violent crimes, accompanied by a body odour that they were told belonged to the perpetrator.

They also watched neutral videos, with a similar setup. Then they identified the criminal's body odour from a lineup of five different men's odours, showing correct identification in almost 70 per cent of cases, researchers said.

"It worked beyond my expectation. Most interestingly - participants were far better at remembering and identifying the body odour involved in the emotional setting," said Olsson.

He tested the limits of our nose-witness ability. Researchers conducted the same experiment but varied the lineup size - three, five and eight body odours, and the time between observing the videos and undertaking the lineup - 15 minutes up to one week.

In lineups of up to eight body odours, participants were still able to distinguish the criminal.

The accuracy of their identification did reduce with the larger lineup size, which is in line with studies on eye and ear-witnesses, researchers said.

The results also show that the ability to distinguish the criminal's body odour is significantly impaired if the lineup is conducted after one week of having smelt the offender's body odour, they said.

"Our work shows that we can distinguish a culprit's body odour with some certainty. This could be useful in criminal cases where the victim was in close contact with the assailant but did not see them and so cannot visually identify them," said Olsson.

The findings were published in the journal Frontiers in Psychology.