Witnesses have always been vital in identifying criminals. Most police lineups require eye-witnesses to identify suspects through visual recognition and ear-witnesses through voice recognition. Now a study shows that nose-witnesses could join the process.
Research published last month in Frontiers in Psychology has found that nose-witnesses can be just as reliable as eye-witnesses in criminal identification.
“Police often use human eye-witnesses, and even ear-witnesses, in line-ups but, to date, there have not been any human nose-witnesses,” Professor Mats Olsson, experimental psychologist at the Karolinska Institutet in Sweden says in a press statement.
Identifying criminals through smell has typically been done by dogs, and human sense of smell is inferior to many other mammals. Numerous studies have shown that the percentage of dog success rate at matching human odour samples to individuals is 75–90 per cent. Swedish researchers have now found that human nose-witnesses’ identification rate in a five sample line-up was between 55-68%, which was “unexpectedly high”.
Human sense of smell is closely tied to areas of the brain associated with emotion and memory, so smell detection is often associated with emotional processing.
To examine human odour memory after stressful events, Olsson and colleagues looked at how well people identify body odour (BO) in a forensic scenario. The study participants watched clips of real, violent crimes while sniffing body odours from wide-mouthed glass jars with the following instructions: “You will see a real crime captured by a video camera. During the video you will be exposed to an odor collected from the perpetrator of the crime you will be watching.”
After watching the clips, the participants were asked to identify the criminals from a line-up of BO samples, one of which was the 'culprit' smell presented as they were watching the video. In line-ups of three, five, and eight samples the participants had a success rate of 96%, 56%, and 46% respectively, and in all cases the results were better than chance.
“It worked beyond my expectation,” says Olsson. “Most interestingly – participants were far better at remembering and identifying the body odour involved in the emotional setting.”
To see whether odour identification was preserved in memory, the researchers also did an experiment increasing the time elapsed between watching the videos and observing the line-up. This gap varied from 15 minutes to one week.
Larger line-ups saw a decrease in identification accuracy, as did the length of time between the incident and the line-up observation. Anything after one week showed that odour identification was severely impaired.
Ultimately these results suggest that humans can distinguish a person’s body odour with some confidence, and, with limitations in mind, nose-witness line-ups could be considered as a forensic strategy.
“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,” says Olsson.