Combination of two HSI cameras and chemometrics for discriminating bodily, non-bodily, and mixed stains

The visualisation of bodily fluid stains in crime scene evidence is often challenging due to the characteristics of the fluid, the substrate on which they are deposited, or the presence of look-alike substances that may confound the investigators. Hyperspectral imaging (HSI) combines conventional imaging with spectral analysis, enabling the simultaneous visualisation and spectral characterisation of stains. In this study, stains of blood, semen, oral fluid, and sweat, together with seven non-bodily fluid stains and five blood-semen mixed stains, were deposited on nine substrates varying in colour and porosity. All stains were analysed using two hyperspectral cameras operating in the visible-near-infrared and shortwave-infrared ranges. The study aimed to evaluate the discrimination potential of the fused data from both cameras using orthogonal partial least squares-discriminant analysis (OPLS-DA). Both cameras proved useful for the analysis of bodily fluid stains, each offering distinct advantages: The SPECIM iQ was more user-friendly, while the HERA SWIR-2 data provides the chemical fingerprint needed to confirm the nature of the stain, due to the specific vibrational overtones in the shortwave-infrared spectral range. Results demonstrated the visualisation and identification of all bodily and non-bodily fluid stains, as well as their discrimination, irrespective of the substrate. The synergistic value of the visible-near-infrared and shortwave-infrared data fusion is clearly demonstrated, particularly in the analysis of the complex blood-semen mixed stains. These findings highlight the significant potential of combining HSI with chemometric analysis for the detection, visualisation, and classification of bodily fluid stains in forensic investigations.