Hairs, Fibers, and Paint

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Hairs, Fibers, and Paint

• Criminalistics
• Chapter 8

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Hair

• A good indicator of individual identity
• Resistant to chemical decomposition
• Retains structural features over time
• Hair is not an absolute indicator of identity but
  can be a good indicator of identity

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Morphology of Hair

• Appendage of the skin that grows out of a hair
  follicle
• Begins at the hair root embedded in the follicle
  and extends outward into the shaft and ends at
  the tip
• The hair shaft is most commonly tested by
  forensic scientists

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The Hair Shaft 4 Parts

• The cuticle outside covering of hair
• Covered in scales that point toward the tip
• Scales are used in identification of the hair
• Animal V. Human Hair

Coronal Crown Shaped Scales
Imbricate Flattened Scales
Spinous Spiny Scales
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Cuticle Photographs
The cuticle is a translucent outer layer of the
hair shaft consisting of scales that cover the
shaft. This photograph illustrates how the
cuticular scales always point from the proximal
or root end of the hair to the distal or tip end
of the hair.
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Cuticle Photographs
                   Spinous or petal-like scales
are triangular in shape and protrude from the
hair shaft. They are found at the proximal region
of mink hairs and on the fur hairs of seals,
cats, and some other animals. They are never
found in human hairs.
Photomicrograph of the proximal scale pattern in
mink hairs. The imbricate or flattened scales
type consists of overlapping scales with narrow
margins. They are commonly found in human hairs
and many animal hairs.
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The Hair Shaft 4 Parts

• The cortex inside the protective layer of
  cuticle
• Made of cells that are aligned parallel to the
  length of the hair
• Pigment granules that provide color are found in
  the cortex

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The Hair Shaft 4 Parts

• The medulla found in the center of the hair
• Predominant feature of hair
• Can be continuous, interrupted, or fragmented
• Can be different shapes in cross-section and can
  be searched using a database

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Medulla Examples
In human hairs, the medulla is generally
amorphous in appearance, whereas in animal hairs,
its structure is frequently very regular and well
defined.
Photomicrograph of Uniserial Ladder Medulla
Photomicrograph of Multiserial Ladder Medulla
The above examples have a well-defined appearance
and came from a rabbit.
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Medulla Examples
Photomicrograph of Animal Hair with vacuolated
medullae.
Photomicrograph of Deer Medulla with
lattice-shaped medulla.
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Human Medulla Examples
When the medulla is present in human hairs, its
structure can be described asfragmentary or
trace, discontinuous or broken, or continuous.
This figure is a diagram depicting the three
basic medullary types.
Discontinuous Medulla in Human Hair
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Hair Identification Animal Versus Human Hairs
Human hairs are distinguishable from hairs of
other mammals. Animal hairs are classified into
the following three basic types. Guard hairs
that form the outer coat of an animal and provide
protection Fur or wool hairs that form the
inner coat of an animal and provide insulation
Tactile hairs (whiskers) that are found on the
head of animals provide sensory functions
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Hair Identification Animal Versus Human Hairs
Human hairs are generally consistent in color and
pigmentation throughout the length of the hair
shaft, whereas animal hairs may exhibit radical
color changes in a short distance, called
banding.
The medulla, when present in human hairs, is
amorphous in appearance, and the width is
generally less than one-third the overall
diameter of the hair shaft. The medulla in
animal hairs is normally continuous and
structured and generally occupies an area of
greater than one-third the overall diameter of
the hair shaft.
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The Hair Shaft 4 Parts

• The root provides for growth of old and new
  hair
• Three phases of hair growth
• Anagen (up to 6 yrs) root attached to follicle
  for continued growth root bulb is flame-shaped
• Catagen (2-3 weeks) slowed growth root bulb
  has an elongated appearance
• Telogen (2-6 months) hair growth ends and is
  shed root bulb is club-shaped

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Phases of Root Growth
Flame-Shaped Root
Elongated Root
Club-Shaped Root
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Identification and Comparison of Hair

• Most comparisons are human v. animal
• Human-human comparisons are problematic
• Variable morphological characteristics
• Vary from person to person
• Vary within a single individual

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Hair Comparison

• Use a comparison microscope
• Compare with standard/reference samples
• Try to match color, length, and diameter
• Can determine dyed or bleached hair from natural
• Time since coloring can be determined because
  hair grows 1cm per month

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Hair Comparison
Pigment granules are small, dark, and solid
structures that are granular in appearance. They
vary in color, size, and distribution in a single
hair. In humans, pigment granules are commonly
distributed toward the cuticle as shown in Figure
1, except in red-haired individuals as in Figure
2. Animal hairs have the pigment granules
commonly distributed toward the medulla, as shown
in Figure 3.
Figure 1
Figure 2
Figure 3
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Human Hair Identification
Human hair can be identified by racial origin,
body area and other classifying techniques.
Key characteristics serve as racial indicators.
These indicators are generalities and apply
primarily to head hairs. The examiner may
encounter hairs that cannot easily be associated
with a particular racial model because of poorly
defined characteristics, limited size, or
inconsistent indicators. These hairs can be
identified as apparent racial mixtures or as not
classifiable.
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Caucasian Hair Identification
Shaft diameter moderate with minimal variation
(mean diameter for human head hairs - 80um)
Pigment granules sparse to moderately dense
with fairly even distribution Cross-sectional
shape oval
Photomicrograph of Caucasian Head Hair
Photomicrograph of Cross-section of Caucasian Hair
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Negroid Hair Identification
Shaft diameter moderate to fine with
considerable variation Pigment granules
densely distributed (hair shaft may be opaque)
and arranged in prominent clumps Shaft
prominent twist and curl Cross-sectional shape
flattened
Photomicrograph of Negroid Head Hair
Photomicrograph of Cross-section of Negroid Hair
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Mongoloid Hair Identification
Shaft diameter coarse and usually with little
or no variation Pigment granules densely
distributed and often arranged in large patchy
areas or streaks Medulla prominent (often
broad and continuous) Cuticle thick
Cross-sectional shape round
Photomicrograph of Mongoloid Head Hair
Photomicrograph of Cross-section of Mongoloid
Hair
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Hair Comparison

• Highly subjective comparative test
• DNA analysis of hair is a much more reliable
  testing technique

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Individualizing Human Hair

• Nuclear DNA Analysis
• DNA found in the nucleus of the cell
• Must have follicular tag or root structure
  present to test

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Individualizing Human Hair

• Mitochondrial DNA Analysis
• DNA found in cellular material outside of the
  nucleus
• Can be tested without follicle or root structure
• More copies of mitochondrial DNA in cells

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Collection and PreservationOf Hair Evidence

• Must be submitted with an adequate sample of hair
  from the victim of a crime, those entering a
  crime scene, or a suspect
• Hair samples must be obtained from the same parts
  of the body
• Usually involve head or pubic hair

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Collection and PreservationOf Hair Evidence

• Head hair approximately 50 full-length hairs
  needed
• Pubic hair approximately 25 hairs needed
• In rape cases, area must be combed for hair
  transfer and then packaged in a separate envelope

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Collection and PreservationOf Hair Evidence

• Hair must be pulled out of the skin or by
  clipping it at the skin line
• Hair is collected from the victims of suspicious
  deaths at autopsy

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Fibers

• Comprise our fabrics and garments
• Important evidence in incidences that involve
  personal contact
• Homicides, assaults, sexual offenses
• Can also be transferred in hit-and-run cases

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Problems with Fiber Analysis

• Mass production of garments and fabrics has
  limited finding origin points
• It is very unusual to identify fiber evidence
  with a high degree of certainty

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Natural Fibers

• Derived in whole from animal or plant sources
• Animal sources sheep, goats, camels, llamas,
  alpacas, mink, rabbit, beaver, and muskrat
• Plant sources primary source? Cotton

Wool Fibers
Cotton Fibers
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Man-Made Fibers

• Derived from either natural or synthetic polymers
• Most have distinguishable cross-sectional
  patterns
• Examples Rayon, Nylon, Acrylic, Polyester, and
  Spandex

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Identification and Comparison of Man-Made Fibers

• Microscopic comparison using a comparison
  microscope
• Color and Diameter
• Striations and Pitting
• Shape of Fiber in Cross-Section

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Identification and Comparison of Man-Made Fibers

• Dye comparison using a microspectrophotometer
• Not limited by size of sample

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Identification and Comparison of Man-Made Fibers

• Chromatography
• Separate shades of color on a chromatograph

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Identification and Comparison of Man-Made Fibers

• Test chemical composition
• Fibers are separated into classes
• Light Analysis
• Light passing through a fiber will be polarized
  and have a specific index of refraction
• Refraction indexes can be compared

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Problems with Fiber ID

• Fiber strands cannot be linked with any certainty
  to any single garment or origin
• Due to mass production of clothing, carpets, and
  other fiber sources

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Importance of Fiber Evidence

• Circumstances of the case
• Other evidence that may link the suspect to the
  scene
• Location, number, and nature of fibers examined
• Judgment of the experienced examiner

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Collection and Preservation of Fiber Evidence

• Fiber evidence often cannot be seen with the
  naked eye
• Fiber evidence can be associated with any type of
  crime and items must be packaged separately

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Packaging of Fiber Evidence

• Articles of clothing must be packaged separately
  in paper bags
• Carpets, rugs, and bedding must be folded
  carefully to preserve fiber evidence
• Car seats must be covered in plastic sheets
• Knife blades should be covered to protect fibers
  that may be stuck to them

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Packaging of Fiber Evidence

• If fibers are to be removed from evidence before
  it goes to the lab
• The possibility exists that the evidence would be
  lost in moving it from the crime scene
• Clean forceps must be used and the evidence
  double enveloped.

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Paint Evidence

• Used in hit-and-run and burglary cases
• Often two or more samples are examined to
  determine a common origin

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Automobile Paint Layering

• First Layer Electrocoat Primer
• Provides corrosion resistance to steel
• Second Layer Primer Surfacer
• Hides any seams or imperfections in the
  automobiles body
• Third Layer Basecoat
• Color of the automobile
• Fourth Layer Clearcoat
• Improves gloss, durability, and appearance

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Examination of Paint

• Basecoat (color layer) provides the most evidence
  because of paint chemical composition
• Layering of paint also helps forensic scientists
  determine a common point of origin

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Value of Paint Examination

• Chemical composition of different paints can be
  linked to different makes and models of
  automobiles and can assist in locating a suspect
  vehicle

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Collection and Preservation of Paint Evidence

• Loose paint chips can be picked up with forceps
  and placed in envelopes or tight-lid containers
• Reference samples must be taken in an area
  adjacent to the missing paint chip by using a
  scalpel or razor blade