Solving cold-cases: Dogs can match human scents collected several years apart – Presented by Margot Perez

Human scent identification line-up is a forensic technique using the remarkable olfactory abilities of dogs to compare trace scents (TS) collected at 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. To our knowledge, 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, we used human scents differing, or not, in terms of collection time, and we subjected dogs to scent identification line-ups early or late after the scent collections. The experiments were carried out with comparisons of TS with BS and with comparisons of BS with BS. We 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. Yet, the dogs’ success rate was above chance in all conditions. Taken together, our 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.