Perez Studies Reveal Dogs May Help Identify Crime Suspects

IWDA Member Margot Perez, who since 2017 has held a researcher position at the National Forensic Police Department in Ecully, France, is studying whether dogs can help law enforcement identify a guilty perpetrator in a police line-up through body scent collected at a crime scene.

While, as Perez stated in her IWDC 2021 presentation, “There is a legitimate possibility for dogs functioning as forensic crime fighters, but more research needs to be done,” an interesting use of a trained dog’s advanced olfactory sense for this purpose is a definite possibility.

Just think how this could have helped Inspector Clouseau.

Perez, who earned her master’s degree in neuroscience, cognition, and ethology at the University of Toulouse (France) in 2011, and, in 2013, a Ph.D. in the Laboratory of Experimental and Comparative Ethology, University Paris 13 in Villetaneuse, France, carried out research into animal behavior, focusing on the effect of the chemical characteristics of odorant molecules and of the olfactory experience on odor perception in ants.

In 2017, she moved on to investigating factors influencing the dogs’ performances in human scent identification line-up in her present position. Perez explains, human scent line-up identification could be a forensic technique using the remarkable olfactory abilities of dogs to compare trace scents (TS) of an individual collected at the crime scene with the body scents (BS) of suspects.

The validity of this method relies on the hypothesis that the human scent is stable over time, as suspects are usually apprehended after the crime commission. In addition, the procedure requires the TS and the BS to be simultaneously presented to the dog, therefore the TS must be stored, awaiting the suspect’s BS collection.

Perez agrees, “the ability of dogs in matching time-lagged human scent collections has never been formally demonstrated and little is known about the effect of scent ageing on dogs’ identification performances.”

Aiming at filling these gaps, Perez and her group used human scents differing, or not, in terms of collection time, and subjected dogs to scent identification line-ups early or late after the scent collections. The assumption each individual human has unique body odor was also made.

The experiments were carried out with comparisons of TS with BS and with comparisons of BS with BS. It was found that a delay between scent collections decreased the dogs’ success rate in the former but not in the latter case and that scent ageing lowered the identification performances in both cases.

Her studies showed the dogs’ success rate was best in comparing TS primary odor with primary BS. Other factors, such as contamination from other odors in stored TS samples can affect the dogs’ performances. The dog, in matching the TS to collected BS is given five choices. It is told to lay down beside the TS scent that matches the BS. Overall, the dogs’ success rate was above chance in all conditions. Taken together, Perez and her group’s results provide strong support for the use of canines in the forensic analysis of human scent as they illustrate the stability of human scent over time and the capacity of dogs to succeed in such comparisons.

By Jed Weisberger