The detection of blood by human remains detection (HRD) canines and blood detection dogs (BDDs) is crucial to both search and rescue (SAR) and crime scene investigation. They can be used to find both missing persons and to detect otherwise undetectable blood evidence at crime scenes. An added level of difficulty with training occurs as blood volatile organic compounds (VOCs) are drastically affected by time. Previous studies have shown this, with a focus on a longer timescale (weeks/months). Little data exists on the changes in the first 48 h, the most crucial time in SAR, something this study aims to rectify. Data was collected using headspace solid-phase microextraction/gas chromatography–mass spectrometry, which was then analyzed using chemometrics and confirmed with canine trials. The results of the laboratory analysis indicated that there were multiple, distinct odor profiles between the 1 h and 2-week time windows—namely, the fresh, intermediate, and aged stages of decomposition. The noted changes in the odor profiles were validated with HRD canine trials. Canines had difficulty detecting the fresh blood (1–2 h old) and had the greatest detection rate for the aged blood (34–36 h old). Both the chemical analysis and canine behavior data displayed a clear change in the odor profile within the first 48 h. This information will assist SAR, HRD, and BBD training to ensure they train on all distinct odor profiles.
Whaley et al. (2025) studied this question.