Photographs of the textile samples pegged on the wire fences submerged in the flumes. B & C: fleece squares; D & E: carpet squares. Credit: https://doi.org/10.1016/j.forsciint.2023.111818.
A new study by researchers at Staffordshire University (UK) may have forensic experts rethinking their evidence recovery approach when it comes to fabrics underwater.
According to a 2020 survey by The European Network of Forensic Science Institutes, a majority of crime scene professionals believe that after 7 days of exposure in an aquatic environment, there would be no fibers remaining to recover as possible evidence. Therefore, institutional and agency protocols are to not search and recover this form of evidence after this time.
However, this first of its kind study shows that is a hasty decision. The newest results show that after four weeks of being submerged in a body of water with constant flow, the lowest percentage of remaining fibers was 33.4%.
“This clearly indicates that it is extremely valuable to search for fiber evidence even after a long exposure time,” said study author Claire Gwinnett, professor of forensic and environmental science at Staffordshire University.
A novel approach
To date, very few studies have investigated fiber persistence on fabrics submerged underwater. The dynamic nature of aquatic environments makes it so studies are difficult to conduct in situ and variables, such as water flow rate, are not possible to control.
That’s why, for this study published in Forensic Science International, the team chose to employ artificial streams, known as mesocosms. Mesocosms are commonly used for ecological research, but this is the first time they have been leveraged for forensic research.
The researchers tested three textiles—woolen/nylon mix carpet, 100% polyester fleece, and 95% polyester/5% elastane sports vest—at two water flow rates over a four-week period.
For both high flow rate and low, there was a high initial loss of fibers in the first 24 hours—up to 81% for low flow rate and 70% for high flow rate—regardless of textile. After 24 hours, however, the persistence rates for both water flows plateaued, while the effect of textile type came into play around hour 48.
The study results show persistence being highest on carpet and lowest on the sports vest, correlating with their respective roughness of surface texture. These textiles continued to demonstrate this same hierarchy of persistence for the remaining exposure times. Additionally, regardless of flow rate, the textile types keep the same order of highest to lowest persistence over 4 weeks, illustrating the overarching effect of fabric construction.
After 4 weeks, the lowest percentage of remaining fibers was 33.4%—fleece material in high flow water conditions.
“Our findings could change how police direct investigations and help to uncover forensic evidence that was previously thought to be lost,” said Gwinnett. “We hope this will help investigators to identify more suspects and ultimately lead to more convictions.”
Given the success of mesocosms in this forensic fiber recovery research, Gwinnett and team say they hope to see the technique leveraged to investigate other types of trace evidence, including gunshot residue, pollen, fingerprints and even DNA.