Dogs and their incredible sense of smell are now being used for all sorts of things, from sniffing out breast cancer to smelling bodies hidden below meters of water. But they are also used by the French police in a different way, to determine whether or not someone was at the scene of a crime. Yet, the use of different training techniques and concerns over reliability have meant that evidence gathered by the canine colleagues is frequently treated with doubt.
A new study looking into the dogs' ability to match a scent sample to a suspect, however, has found that the trained animals can get it right 80-90 percent of the time. Critically, they were found to never match the wrong person to the wrong sample. The researchers hope that their findings, published in PLOS ONE, will validate the technique, and motivate more police forces to adopt the procedure.
Whenever you touch something, or sit somewhere, you leave your odor on the surface of the objects. Made up of differing ratios of volatile chemicals, each person’s individual scent is unique and stays relatively constant over time. It’s thought that this scent can persist on the objects for up to several days, meaning that if it can be detected, it could in theory link an individual to a certain location if collected within the correct time period. This is where the dogs come in.
Forensic experts "collect" scent samples from objects, even those that have only been touched for a matter of minutes. Xavier ROSSI/Getty
A dog’s sense of smell is astonishing. Estimates put it at over 1,000 times better than ours, though some rate it much higher than this as where we have around 5 million scent receptors in our noses, a German shepherd has roughly 225 million. To use it in a crime-busting capacity, forensic experts “collect” scents from the scene of a crime. This can be in the form of an object, such as an item of clothing or mobile phone, or cotton pads that are placed on surfaces to “pick-up” the smell that is left behind. These scents can even be stored in sterile conditions for long periods of time.
The police then collect an odor sample from the suspect or victim, as well as from a few other people not thought to be involved with the case, and place them in jars. The dog then smells the sample “evidence” scent collected at the scene, and is then allowed to have a good whiff of the other odors. When the smells match, the animal is trained to sit or lie down at the correct sample.
The researchers found that after a training period of 18-20 months, the dogs were able to do this with an impressive 85 percent accuracy, with the other 15 percent being attributed to an inadequate evidence scent for the dogs to sniff. In practice, each identification test is carried out by at least two dogs, and each dog carries out at least two tests using the same panel of scents.
The study seems to validate the ability of the dogs to successfully match the suspect to the scene, so long as they are trained in a recognized way. The researchers hope that other police forces might be able to now use these techniques, and that the evidence can be given better credence.