Despite being only 45 to 60 per cent accurate, the eyewitness line-up is still a standard procedure in many courts around the world.
The trauma associated with a violent crime often makes victims unable to remember what the perpetrator looked like, often leading to a false positive – the conviction of a non-guilty suspect.
In a new study, just released in the journal PLOS ONE, researchers tried to find out whether our sense of smell might help us pick out violent offenders with greater accuracy.
As has been known for centuries, different smells can evoke an instantaneous flood of memories – a feat that other human senses are not nearly as good at.
This linkage between scent and emotion can be explained by the fact that the olfactory bulb – a neural structure in the forebrain responsible for detecting smell – is part of our limbic system, an area so closely associated with memory and emotion that some feel inclined to call it the “emotional brain”.
Past studies have shown that each of us has a distinctive smell which stems from a combination of hormonal patterns, diet and even parasitic infections.
“Every individual has a unique body odour (BO), similar to a fingerprint,” wrote the researchers. “In forensic research, identification of culprit BOs has been performed by trained dogs, but not by humans. We introduce the concept of nosewitness identification and present the first experimental results on BO memory in witness situations involving violent crimes.”
First, the research team took body odour samples from 20 healthy male volunteers, while they worked on a non-stressful assignment over a period of 2 hours and 30 minutes. The subjects were asked to refrain from doing anything that might alter their baseline BO before and during the sampling.
Then they randomly assigned 80 students (40 males and 40 females) from the University of Aveiro, Portugal to one of two conditions: “nosewitness” and neutral.
In the former, subjects watched a short video of a violent crime, while being primed with an odour sample. They received “written instructions aimed to get the participant in the mindset of a witness to make the experimental model of the nosewitness situation more realistic.”
In the neutral condition, students were presented with the same body odour, but shown an emotionally neutral video and neutral instructions.
After analysing the data, researchers concluded that those who were assigned to the nosewitness condition were able to identify the perpetrator 75 per cent of the time.
“Our results suggest that humans are capable of identifying a culprit by way of odour. When the perpetrator and the victim are close to one another, as in crimes of sexual and physical assault, and especially under visually obscure conditions, an olfactory cue may be the prevailing detail.”
Even though the experiment was carried out in a clinical environment, the robust result should prompt further research to help devise a formal procedure.