Volatile organic compounds: instrumental and canine detections link an individual to the crime scene

Background: Whenever a crime is committed, forensic personnel are requested to collect every kind of evidence to establish the relationship between the suspects and the crime. When any evidence is accidentally destroyed or not found, there is one type of latent evidence that is always deposited at the crime scene: unique human scent. Recently, the use of trained canines to detect selective human scent at a crime scene has increased. To consolidate this kind of evidence, it is essential to have an exact knowledge and an awareness of the chemical signature of the volatile compounds that could indicate the presence of the alleged offender at the crime scene. This experimental study aims to detect the volatile organic compounds (VOCs) released from subjects who handled scent-articles to imprint their odor on. After handling, each scent-article was wrapped in sterile and VOC-free cotton gauzes for 48 h for secondary transfer. VOCs were detected by headspace/solid-phase microextraction-gas chromatography/mass spectrometry (HS/SPME-GC/MS) and well-trained dogs, at different time points (up to 15 days). Furthermore, the possibility of further DNA detection after contact was also investigated to propose a novel approach able to identify a subject from this latent forensic trace. Results: Data show that inter-individual human scent composition includes different VOCs, but dogs were able to discriminate the individual who touched the object at the crime scene. The dog training procedure showed excellent sensitivity (between 99.48 and 100%) and specificity (between 60 and 100%), having a positive predictive value (PPV) ranging between 97.94 and 100% and a negative predictive value (NPV) ranging between 85.71 and 100%. Preliminary work on DNA analysis released after contact yielded positive results, even if further studies are necessary, expanding the same experimentation to a larger sample with the aim of obtaining a statistically significant result. Conclusion: Data show that human scent is a good source of VOCs and a good target for canine training. The well-trained dog represents a specialized biological device able to discriminate personal human odor from any contaminants in the mixture detected by instrumental analysis. Furthermore, this study proposes the use of human scent as a forensic latent trace for DNA profiling.