Chapter 11: Hairs and Fibers in Forensics

Hairs and Fibers in Forensics explains the three developmental stages of hair growth—anagen, catagen, and telogen—and emphasizes that the anagen phase is most likely to yield a follicular tag rich in nuclear DNA, which allows for individualization, whereas the hair shaft typically contains only mitochondrial DNA inherited maternally. The discussion covers the determination of racial origin, somatic origin, and whether hair was forcibly removed, alongside the importance of collecting adequate reference samples (such as 25 full-length hairs) to account for intra-individual variation. Transitioning to fibers, the chapter classifies them into natural fibers derived from plants and animals, such as cotton and wool, and manufactured fibers, which are further divided into regenerated fibers like rayon and synthetic fibers like nylon and polyester composed of long-chain polymers. The text outlines analytical techniques including the use of the comparison microscope for examining color and diameter, the visible-light microspectrophotometer for spectral dye analysis, and thin-layer chromatography for separating dye components. Furthermore, it describes how infrared spectrophotometry and the polarizing microscope are utilized to determine generic classes and optical properties like birefringence and refractive indices. Finally, the chapter underscores the probabilistic nature of fiber evidence as class characteristics, illustrated by high-profile cases like the Wayne Williams trial, where the significance of associating rare fiber types with a suspect's environment was pivotal.