Page 10 - Strands of Evidence Hair And Fiber
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of time than in the case of less forceful and intimate growth phase, while the telogen phase is a dormant
encounters. phase, during which growth ceases. The telogen
phase produces the majority of the evidentiary
Because of the transient nature of trace evidence, material since most hairs found at a crime scene
investigators must take care with collection and are naturally shed. Anagen and telogen hairs can
preservation. Additionally, investigators could be distinguished by examining the root sheath,
introduce, through secondary transfer, extra as telogen hairs have characteristic club-shaped
trace materials into a crime scene which could roots, while anagen hairs show stretching of the
contaminate evidence. Equal caution must root area due to the mechanical force required
be taken to avoid inadvertently removing or to remove them from the follicle. The damaged
destroying trace materials from the crime scene. root of an anagen hair is important, as it suggests
As time passes after the completion of a crime the that force was used to remove it and can indicate
likelihood of evidence becoming lost increases. violence.
To prevent contamination or loss concerns,
“elimination standards” are often collected from The root sheath is the base from which the hair
crime scene personnel and used to exclude them shaft grows. DNA can be obtained from the roots
as the source of evidence. First, large evidence of hair, which may contain up to 100,000 cells,
should be collected during a careful walk through however obtaining DNA from the shaft of hair is
of the scene. Next,. trace evidence should be often difficult. Hair shafts contain three layers: the
collected before, finally, the scene is processed medulla (inner), cortex (middle), and cuticle (outer)
for other types of evidence, such as fingerprints layers. The cuticle is translucent and contains
and biological evidence. This procedure ensures scale patterns that cover the shaft, and these
that the most evidence possible will be preserved, scale patterns can be used to define the species
rather than destroyed, during the investigation. of mammal that shed the hair. There are three
basic scale patterns: coronal (crown-like), spinous
Trace evidence, as the name implies, can include (petal-like), and imbricate (flattened). Human hairs
many small quantities of contact-associated usually have the imbricate scale pattern, therefore,
items. The two most common types recovered at when an investigator identifies a hair containing a
a scene are hairs and fibers, an association that coronal or spinous pattern, the likely deduction is
seems natural given the amount of these types that the hair was not shed by a human.
of materials encountered in daily life. Whether
combing hair, sitting on a carpet or rug, or Trace analysts use “scale casting” techniques to
brushing against a household pet, hair and fibers identify hairs as either human or animal. A cast of
are constantly exchanged through normal, day- the scale pattern on a hair is made and examined
to-day interaction. The discovery of hair evidence under a microscope at a range of magnification
at a crime scene could place a suspect in an area between 40X and 400X. One of three techniques
they deny having been in. The type, condition, and is commonly used to make a scale cast. In the
number of hairs found at a scene all contribute to first method, a Polaroid film-coater may be used
their value in a criminal investigation. to apply a thin layer to a glass microscope slide.
A hair specimen is then pressed into the film and
Hairs are comprised of the protein keratin and grow allowed to dry. When the hair is removed, the cast
outward from follicles in the skin of mammals. Hair remains, and this scale pattern is then analyzed
undergoes two main life stages: the anagen and under the microscope to classify the hair. Clear
telogen phases. The anagen phase is the active tape, in combination with a slide cover slip, can
10 THE MYSTERY OF LYLE AND LOUISE
