The detection, or non-detection, of bruises on a victim can have significant implications both medically and legally. Legally, the detection and appearance of bruises plays a pivotal evidentiary role in crimes such as sexual assault and domestic abuse. Studies have shown, however, that victims with dark skin tones are at a significant disadvantage when it comes to properly documenting bruises under regular light. Now, researchers at George Mason University have proposed and tested a solution—alternative light sources.
Dr. Katherine Scafide, a forensic nursing expert at George Mason, and her team designed a randomized controlled trial of 157 adults to measure the bruise detection capabilities of alternate light sources within visible and long ultraviolet spectrums. The study participants were balanced across six skin color categories. Bruises were created under the controlled application of a paintball pellet and dropped weight to one upper and lower arm, respectively.
The researchers used yellow, orange and red colored filters across 10 different wavelengths ranging from 350 (UV) to 535 nm to analyze the bruises 21 times over the course of 4 weeks post-injury. According to the study, published in the Journal of Forensic Sciences, results revealed evidence of bruising was most frequently observed under 415 nm or 450 nm with the yellow filter. Detection at these wavelengths with a yellow filter proved to be 5x higher across all skin tones when compared with regular white light. The 415 and 450 nm orange filter was also effective, but only on the paintball-induced bruises.
The research team also assessed the impact of victim characteristics on bruises, including age, gender and localized fat. The odds of detecting bruises were higher on subjects that were older, even though the median age of the study participants was relatively young at 24 years old. Additional results showed bruises were 3x more likely to be detected on women than men, and participants with more localized fat showed a higher rate of bruise detection.
Unsurprisingly, the ability to detect bruises, regardless of light source, diminished over time—at a rate of 12% ever 24 hours post-injury.
In 2013, the U.S. Department of Justice released “A National Protocol for Sexual Assault Medical Forensic Examinations,” which included guidance on using alternative light sources for examining patients’ bodies, hair and clothing, and urged more research on the topic and “up-to-date technology.” In 2015, the National Institute of Justice’s Forensic Science Technology Working Group requested to make detection of subtle injuries an R&D priority. In the years since, however, not much research has been conducted and/or published regarding alternative light sources.
“Research investigating [alternative light source] application in the clinical detection of bruising has been limited in both quantity and quality. Our study has advanced the science by attempting to use a more rigorous approach in both methodology and data analytics to better understand major factors associated with ALS identification of injuries on diverse skin tones,” the authors write in their paper.
Scafide cautions use in the implementation of alternative light sources as the research is still in its infancy. She plans to continue her line of work through a new grant from NIJ, which will allow her to develop and evaluate much-needed evidence-based guidelines.
Photo: Example of yellow filter alternative light source. Credit: George Mason University