Researcher says subpopulation analysis of fibers can strengthen forensic evidence

Katia Pontevedera, a criminologist and researcher, told conference attendees that detailed subpopulation analysis of textile fibers can increase the strength of fiber evidence in contact-crime investigations.

"They can help determine if two pieces of garments were in contact together," Pontevedera said, describing how fibers transfer between garments and how transfer likelihood depends on contact pressure, surface type and fiber construction. She cautioned that fiber evidence alone does not prove two people had direct contact but said it can meaningfully supplement investigations.

Pontevedera described a population study she carried out in London as part of a master's dissertation at London South Bank University. She said she recovered "almost 3,000 fibers" from 10 seats in a lecture theater and identified 571 fibers used as controls. Using microscopy, FTIR (Fourier-transform infrared spectroscopy) for manmade fibers and microspectrophotometry (MSP) to compare dye spectra, she reported that natural fibers comprised about 82% of her analyzed sample and manmade fibers 18%; within the natural category she reported 79% cotton and 3% wool. The most common color class across the sample was blue (64%).

Focusing on subpopulation analysis, Pontevedera said MSP can distinguish dye-spectral differences within a common fiber class. Because she ran out of time to analyze the large number of blue cottons, she instead sampled 188 red and pink cotton fibers for MSP. From those 188, she said 78 fibers could be grouped into 21 distinct subpopulations, with subgroup sizes ranging from two to 11 fibers; 110 fibers remained spectrally distinct and therefore have higher discriminating power in court.

"If they are from the same garment, they would be [spectrally similar]," she said, describing how matching spectral peaks on MSP traces supports grouping into a subpopulation and can increase evidential value.

Pontevedera argued that because fiber frequency varies by place and season—lecture halls, buses and different cities yield different distributions—jurisdiction- or venue-specific population and subpopulation studies are important for contextualizing how probative a fiber match is in a particular case.

She closed by saying these findings are preliminary, part of a dissertation and not yet published, and offered contact information for follow-up.

The presentation emphasized methods and sample results; no formal votes or policy actions were recorded.