The fibers kept by the bodies of some victims matched those found on the clothes of "Wayne Williams", a suspect in the murders of children in Philadelphia, USA, which led the criminal investigation to solve the mystery of one of the most heinous crimes that shook American society in the eighties, but what if the killer had thrown his victims into waterways, would the fiber evidence have died?
A study led by researchers from the Centre for Crime, Justice and Security at the University of Staffordshire says that "even if criminals did so, the fibre evidence would survive underwater much longer than previously thought," which could help criminal investigators uncover vital evidence.
Forensic examiners had believed that if objects were submerged in water for more than 7 days, any valuable evidence would disappear, but the new study, published in the journal Forensic Science International, refutes this idea and confirms through practical experience that the evidence of fibers can survive underwater for several weeks.
Forensic laboratory analysis of fibers collected from crime scenes, using polarized light microscopy, infrared spectroscopy using the Fourier transform, and fine UV and visible absorption spectrophotometry, which can lead to important information.
Claire Gwinnett, a professor in the Department of Crime, Society and Environment at the University of Staffordshire, and lead author of the study, said in emails to Al Jazeera Net that investigators believe that the dynamic nature of the waterways, in general, makes them an unfriendly environment for evidence, "but we have established a need to refute this hypothesis, focusing on fiber."
Researchers use mesocosm mechanism to study the rate at which polyester fibers hold on different types of fabrics (University of Staffordshire)
What did Claire and her buddies do?
The dynamic nature of aquatic environments means that it is difficult to conduct on-site studies and it is not possible to control variables, such as the rate of water flow, so Claire and her colleagues resorted to a mechanism known as mesocosm, to study the stability rate of polyester fibers on different types of fabrics over a period of 4 weeks.
Mesocosm, any external experimental system that examines the natural environment under controlled conditions, is commonly used in environmental research, and this is the first time it has been used to look at forensic evidence, Claire explains.
During the study, conducted as part of the Criminal Freshwater Fibre project, implemented by the Centre for Crime, Justice and Security at the University of Staffordshire, in partnership with researchers from universities and research centers in Austria, Australia and Italy, Claire and her colleagues used industrial currents with high and low flow velocities, on 3 textiles: "wool-nylon blend carpet", "100% polyester wool piece", and "95% polyester and 5% elastane sports jacket".
The initial fiber loss rates were the highest in the first hour of immersion for carpets, wool and sports jackets, however, the rates remained mostly constant after 24 hours for all textiles, the flow rates used did not significantly affect the stability of the fibers, and even after 4 weeks, the lowest percentage of the remaining fibers was 33.4%.
What do these results mean?
These results clearly indicate that it is extremely useful to look for fiber evidence even long after the textiles have been immersed in water. "By understanding the survival of the fibers on these surfaces, investigators are able to create timelines of when these fibers were moved, a condition that can help connect individuals to items and people at certain time intervals, and this helps reconstruct events," says Claire Gwinnett.
"The mesocosm method, which was used in the fiber test, could be used to test the survival of other forensic evidence such as gunshot residues, fingerprints, DNA and hair, in the dynamic environment of rivers."
"Our next step will be to expand the experiment to include testing the survival of those other forensic evidence, and we're going to recreate the experiment in a real river, compare the results, see if they're comparable to this real environment, and then make further recommendations on the factors we need to consider when retrieving and interpreting evidence."
The study answers a previously unasked question: "How long can fiber evidence remain underwater"? (Shutterstock)
Increase the value of fiber guides
Two experts polled by "Al Jazeera Net" believe that the study and its results reinforced the importance of fiber evidence in forensic medicine.
Tom Schotman, a researcher in the Department of Chemical and Physical Archaeology at the Dutch Institute of Forensic Medicine, said in brief emailed remarks: "Physically, we thought the fibers were unlikely to stay long on submerged fabrics, but the study, which used a comprehensive methodology, shows that they survive longer than often expected."
Matteo Galidapino, a forensic chemistry researcher at King's College London, was impressed by the study's findings, which he said allowed for more use of fibre evidence in forensics.
He says the information that can be found from evidence of the fibers "is generated when people come into contact with each other, in this case, the fibers are usually transferred between them (i.e. between the perpetrator and the victim), and their number, as well as their location on the receiving surface (e.g. clothing), and the type of activity."
"After a physical assault, for example, more of them are transferred between people, compared to after a hug, and the position of the fibers itself may be an indicator of how the assault occurred, which is why fibrous evidence is usually used to help investigate a crime, and it is often also presented to the court, through which forensic scientists can provide evidence of the intensity of a particular contact between two people, and then distinguish between assault or any other type of interpersonal contact. When a body is found, fibrous evidence may be useful for understanding whether or not it was the result of a direct attack, and it can also provide a link to a specific source (clothing), thus providing evidence that someone was at the crime scene."
The most important value of the study, according to Galidapino, is that it answers a question that has never been asked before: "How long can the evidence of fibers remain underwater?" "This work particularly delves into this issue and systematically examines the impact of various influencing factors, such as water flow rate and type of receiving surface, on the stability of the fiber index," he says.