An Assessment of Decomposition Training Aids Under Freezing Conditions

Scent detection canines have grown to play a vital role in multiple law enforcement agencies for various reasons. A particular class of scent detection canines is referred to as human remains detection (HRD) canines—also commonly referred to as cadaver canines. To maintain the canine team at optimal performance and ready for deployment scenarios, it is vital that canine handlers make use of training aids at distinctive stages of putrefaction to train the canine to the whole spectrum of decomposition products that can be encountered in operational deployments. During the complex decomposition process, volatile organic compounds (VOCs) are emitted, and recent research studies have been underway to identify the types and amounts of distinctive compounds under different environmental conditions and decomposition stages from both human and animal models. Understanding the definition of the cadaveric odor profile can help better train canine detection teams as well as help with technological developments. Considering that the training aids can be difficult to acquire, handlers typically reuse the training aids for prolonged periods of time until new materials are available—this period can be anywhere between several months to years. When not being used in search assessment scenarios, the training aids are stored under refrigerated conditions until they are needed again. Therefore, it is imperative to have a deeper understanding of how the VOC profile of training aids is affected by refrigerated conditions as a function of storage time. The objectives of this research were to: 1) monitor chemical odor profiles utilizing two containment vessel types (clear and amber vials) across a 6-week period, and 2) monitor two preservation methods (continuous and preserved) on chemical odor profile changes as a function of freezing to thawing cycle conditions. Instrumental analysis used Divinylbenzene/Carbon/Polydimethylsiloxane (DVB/CAR/PDMS) coated Solid Phase-Microextraction (SPME) fibers along with a Gas Chromatography-Mass Spectrometry (GC-MS) system for the identification of volatile odor compounds (VOCs) from tissue/bone samples of pig carcasses at the fresh, advanced decay and skeletal stages of decomposition. Samples were instrumentally analyzed each week for a total of six (6) weeks to monitor the chemical odor profile as a function of time. Each stage of decomposition portrayed distinct chemical odor profiles, with alcohols and carboxylic acids being the most prevalent across the board, but with varying abundances per stage. In terms of containment vessel type, the more favorable vial varied between stages of decomposition, as the clear vial was optimal for the fresh stage, but the amber vial was optimal for the advanced decay and skeletal stages. Regarding the preservation methods in which the freezing-thawing routine of the samples changed, the continuous preservation method portrayed better reproducibility of the original odor profile throughout the 6-week analysis period as depicted from higher Spearman correlation values. This research will aid to understand the behavior of VOC profiles of decomposition training aids and how to better preserve them for effective canine training.