Degrees of contrast: Detection of latent bloodstains on fabric using ALS and the effects of washing




James, Matthew E.

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Bloodstains are a useful piece of evidence for solving many crimes. The DNA analysis of bloodstains deposited on a piece of clothing can identify whose blood is on the clothing and may place a subject at the scene. In some cases, the stain’s shape, and overall pattern, can provide much more information. However, it is particularly difficult to identify bloodstains on dark clothing and clothing with patterns. Current methods to detect these stains include advanced photography techniques with Alternate Light Sources (ALS) or the use of chemicals that react to the hemoglobin and fluoresce. Photography methods are non-invasive, but there is little research on what wavelengths are the most effective. Chemicals such as Luminol, Bluestar, and Fluorescein are effective, but ultimately ruin the pattern and prevent morphology interpretation of the stain. This study explores the use of ALS to photograph bloodstains in order to provide an alternative non-invasive tool before the use of chemical detection techniques. This study examined whether blood always absorbed light in the 300nm to 900nm range and the best wavelength for observing blood on dark and or patterned fabrics. It also explored whether fabric type, fabric color, or pattern affected the ability to view blood on fabrics, if washing the fabric affected the use of ALS, and, if so, to what extent. Sixty-nine fabrics were photographed in monochrome under ambient light, and then with and without filter under 350nm - 380nm (UV), 400nm - 430nm (Violet), 430nm - 480nm (Blue), 480nm - 560nm (Green), and 800nm - 900nm (Infrared) light. Each photograph was bracketed to ensure the best exposure and contrast between the stain and fabric. In total, 33 photographs were taken for each fabric after each wash cycle. Contrast was measured between the bloodstain and the fabric using ImageJ software to measure the effectiveness of each wavelength. 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, were the most effective light sources for viewing bloodstains on dark fabrics without the use of chemicals.



Blood forensics


James, Matthew E. (2020, 1 May). Degrees of contrast: Detection of latent bloodstains on fabric using ALS and the effects of washing.