Degrees of contrast: Detection of latent bloodstains on fabric using an alternate light source (ALS) and the effects of washing

Blood is often a piece of evidence of violent crimes and will often be on the perpetrator's clothing. If the perpetrator is wearing dark clothing, it can be easily identified by chemical means such as Bluestar (R), but this can destroy the pattern, which may be evidentiary itself. This study explores the use of alternate light source (ALS) to photograph bloodstains on dark and/or patterned fabrics to provide an alternate, noninvasive tool before the use of chemical detection techniques. Sixty-nine (69) unwashed fabrics, of various dark colored and dark patterns, were photographed in monochrome under ambient light and subsequently with and without a filter under ultraviolet (UV), violet, blue, green, and infrared light. This study used ImageJ to measure the contrast between the bloodstain and the fabric and thus the effectiveness of each wavelength. Each fabric was washed, photographed, and analyzed five times or until the bloodstain was no longer visible under ALS. Results indicated photography with ALS was a viable method for blood detection on fabrics and should be used prior to chemical means. Further, infrared, followed by violet light with no filter, was the most effective light source for viewing bloodstains on dark fabrics without the use of chemicals. However, these wavelengths were not effective on military uniforms. This study also described one effect fabric manufacturer chemical treatments have on bloodstains and the effect of washing fabrics with bloodstains.

Automated summary

The study investigated the use of alternate light source photography for bloodstains on fabrics, finding it to be a viable method before chemical detection. Infrared light, followed by violet light without a filter, was found to be the most effective for viewing bloodstains on dark fabrics without chemicals.