Page 12 - Strands of Evidence Hair And Fiber

Hair, in both humans and animals, is influenced to densely packed that occur at even intervals. If
by which body region it grows in. These differing these hairs are cut, cross-sectional views reveal
characteristics may be used to determine the oval shapes. African origin hairs have a wide range
hair’s origin on the body. In humans, while it is of shaft diameters, from moderate to fine, and the
possible to identify chest, arm pit (axillary), or shafts of these hairs have prominent twisting and
limb hairs, they are rarely recovered as evidence curling with pigment granules densely distributed
at a crime scene. The primary types of human hair throughout. This dense pigmentation gives
used in forensic investigations come from either the hairs an opaque appearance when viewed
the scalp (head) or pubic regions. Scalp hairs are through a microscope. The cross-sectional shape
generally longer with a moderate shaft diameter; of these hairs is flattened. Asian origin hairs
the medulla in human head hair ranges from have coarse shaft diameters with little variation,
completely absent to continuous and is narrow densely distributed pigment granules arranged
in comparison to hairs from other portions of in patchy areas or streaks, broad and continuous
the body. Pubic hairs are more coarse and wiry, medullas, thick cuticles, and round cross-
often exhibit characteristic “buckling” of the shaft, sectional shapes.
and frequently have broad, continuous medullas
throughout. Hair comparisons do not provide absolute
identification. A trace evidence examiner, however,
The structure of animal hair is often dependent on can reach one of three basic conclusions from hair
the hair’s function. Guard hairs form an outer coat comparisons:
of many animals, providing protection, while the fur
or wool hairs of the inner coat provide insulation. 1. Hairs from the suspect or known source have
Additionally, the tactile hairs or whiskers are used the same microscopic characteristics as the
as sensory devices. evidence, and these samples can be associated
with one another.
Furthermore, scalp hairs frequently show
characteristics from grooming, such as artificial 2. Hairs from the evidence are microscopically
coloring, bleaching, or tips that are cut or split. different from the hairs from the known
Hairs generally grow one half-inch per month, suspect or source, and these samples cannot
therefore hairs may give an investigator the be associated with one another.
opportunity to measure the amount of time
between an event (such as dyeing of hair) and the 3. Hairs from evidence have some
time the hair was left at a scene. characteristics that match and some that do
not match the known suspects or standards,
In addition to identifying a hair’s original location therefore no conclusion can be drawn as
on the body and differentiating human from to whether the samples are from the same
animal hairs, human hairs can be classified into source.
three ethnic or racial categories: European origin
(Caucasian), African origin (Negroid), or Asian/ When reaching these conclusions, an analyst
Native American origin (Mongoloid). European should limit the report to only factual items and
origin hairs normally have moderate shaft not interpretations. Interpretations of evidence and
diameters (~80 μm) with minimal variation and its relationship to a crime should be left for court
pigment granules ranging from sparse in number testimony.

12 THE MYSTERY OF LYLE AND LOUISE