Detection of body fluids on clothing in sexual assault cases: forensic applications of multispectral imaging systems

In sexual assault investigations, the rapid and accurate localization of biological traces on clothing is important for guiding evidence collection and preserving forensic material. Multispectral imaging systems provide a non-invasive optical approach for visualizing body fluids that may be difficult to detect under conventional lighting conditions.

Seven biological fluids-venous blood, menstrual blood, semen, vaginal secretions, urine, saliva, and sweat-were applied to cotton and synthetic fabrics of different colors and textures. After air-drying, the samples were examined using three portable multispectral imaging devices: Forenscope Multispectral SAFE/Colposcopy, Safe Pro Smartphone, and Mobile Multispectral Tablet. Stain visibility was initially assessed using a predefined ordinal visual scoring system. In addition, post hoc quantitative image analysis was performed on exported image files by calculating signal intensity, background intensity, contrast, and signal-to-noise ratio (SNR).

On light-colored fabrics, most biological fluids were readily detectable under white or visible light. On dark fabrics, infrared illumination provided improved stain-background separation, particularly for blood and semen. Semen, vaginal secretions, and saliva showed visible fluorescence under blue light in the 440-470 nm range combined with an orange filter. Quantitative analysis demonstrated significant differences in contrast and SNR according to imaging device and fabric color, whereas fabric type did not show a significant effect. Biological fluid type significantly affected contrast, but not SNR.

The detectability of biological fluids on clothing depends on fluid type, fabric characteristics, and spectral imaging conditions. Portable multispectral imaging systems may support the rapid, non-destructive localization of biological traces in forensic examinations. However, the present study should be interpreted as an exploratory evaluation under controlled conditions, rather than as diagnostic validation or evidence of superiority over conventional forensic detection methods.