Forensics: Chapter 8

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Forensics Chapter 8

• Hairs, Fibers Paint

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Objectives

• Describe techniques for describing, identifying,
  and differentiating samples of human and
  non-human hair.
• Describe techniques for describing, identifying,
  and differentiating samples of fibers.
• Describe techniques for differentiating samples
  of paint chips.

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Hair, Hair, Everywhere!

• It is not yet possible to individualize a human
  hair to any single head or body through its
  morphology.
• However, hair does have evidentiary merit.
• When collected properly and submitted to a
  forensic laboratory with an adequate number of
  standard/reference samples, hair can provide
  strong corroborative evidence for placing an
  individual at the scene of a crime.

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Parts of a Hair

• Root or bulb (embedded in a hair follicle)
• Shaft
• Tip

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Hair Shaft

• The shaft portion of the hair is subjected to the
  most intense examination by forensic scientists.
• Parts of the Shaft
• Cuticle outside covering of hair
• Cortex main body of hair shaft
• Medulla center column of hair

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Cuticle

• The cuticle is primarily responsible for two
  features that make hair a good subject for
  establishing identity of an individual
• 1. chemical decomposition (most resistant)
• 2. ability to retain structural features
• The cuticle is formed by overlapping hardened
  (keratinized) scales that always point toward the
  tip of the hair.

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Good to Know

• The scales of animals have a variety of patterns
  that make them helpful in distinguishing among
  species of animals. (see Figure 8-2)
• Shaft length of hair is MOST important for making
  species comparisons.
• A cast of a hair surface can be made by using a
  soft medium such as softened vinyl or clear nail
  polish.

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Cortex

• The cortex is the main body of the hair shaft.
• The cortex is contained within the protective
  layer of the cuticle.
• The cortex is embedded with pigment granules that
  impart hair with color. Color, shape, and
  distribution of these granules provide a
  criminalist with important information that
  allows them to compare against the hairs of
  different individuals.

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Medulla

• The medulla is a cellular column (central canal)
  running through the center of the hair.
• The medulla is the dominant feature comprising
  more than half of the hairs diameter.
• The medullary index measures the diameter of the
  medulla relative to the diameter of the hair
  shaft and is normally expressed as a fraction.
• Medullary indices for humans generally have a
  value of less than one-third or may be absent
  entirely for most other animals, the value is
  one-half or greater.

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Medulla (cont)

• The presence and appearance of the medulla vary
  between individuals and among the hairs of a
  given individual (two hairs from the same head
  may not have the same morphological
  characteristics).
• Medullae can be classified as continuous,
  interrupted, fragmented, or absent (see Fig 8-3)

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Medulla (cont)

• Medullae can be classified as continuous,
  interrupted, fragmented, or absent (see Fig 8-3)
• Humans generally have no medullae or have
  fragmented one
• (exc Mongoloid race which
  are continuous)
• - medullae is nearly cylindrical in
  appearance
• Animals generally exhibit medullae that are
  either continuous or
• interrupted.
• Medullae can be vary in shape
• ex cat string of pearls
• ex deer spherical cells
  along entire hair shaft

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Root

• Human head hair grows in 3 developmental stages.
  
• Rate of human hair growth per month is 1 cm.
• The shape and size of the hair root is determined
  by the growth phase in which the hair happens to
  be.

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3 Developmental Hair Stages

• Anagen
• Catagen
• Telogen

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Anagen Phase

• Initial growth phase during which the hair
  follicle is actively producing hair.
• May last up to six years
• Root is attached to the follicle giving the root
  bulb a flame-shaped appearance
• When pulled from the root, anagen hairs will
  contain a follicular tag (translucent piece of
  tissue surrounding the hairs shaft near the
  root. It contains the richest source of DNA
  associated with hair).

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Catagen Phase

• Transition stage
• Hairs continue to grow but at a
• decreasing rate
• May last from two to three weeks
• Roots typically have an elongated
• appearance (root bulb shrinks and is
  
• being pushed out of the hair follicle).

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Telogen Phase

• Final growth phase in which hair naturally falls
  out of the skin
• Root takes a club-shaped appearance
• During a 2 to 6 month period, the hair will be
  pushed out of the follicle causing hair to be
  naturally lost.

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Identification and Comparison of Hair

• Usually when hair evidence is present in a
  criminal case, the primary purpose for its
  examination is to determine if the hair is human
  or animal in origin (generally not very difficult
  to ascertain) or whether human hair retrieved at
  a crime scene compares with hair known to have
  come from a particular individual.

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Forensic Hair Considerations

• When comparing hair, the criminalist is
  particularly
• interested in matching the following
• color
• length
• diameter
• presence or absence of medulla
• distribution, shape, and color intensity of the
  pigment granules in the cortex
• morphological abnormalities (due to certain
  diseases or deficiencies)
• presence of fungal and nit infections

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Can The Body Area From Which A Hair Originated Be
Determined?

• Scalp Hair little diameter variation and more
  uniform distribution of pigment color as compared
  to other body hairs.
• Pubic Hair wide variations in shaft diameter
  and usually have continuous medullae
• Beard Hair normally triangular in cross section
  with blunt tips due to shaving

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Can the Racial Origin of Hair Be Determined?

• All observations are general with many possible
  exceptions.
• Africoid hair is kinky,
• - contains dense, unevenly distributed
  pigments
• - cross section of hair is flat to oval
  in shape.
• Caucasian usually straight or wavy
• - fine to coarse pigments that are more evenly
  distributed than Africoid hair.
• - cross section of hair is
  oval to round in
• shape

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Can the Age and Sex of an Individual Be
Determined from a Hair Sample?

• Age cannot be determined with any degree of
  certainty (except with infant hair)
• Sex recovery of nuclear DNA from either tissue
  adhering to the hair or from the root structure
  will allow for sex determination.

22
Is It Possible to Determine If Hair Was Forcibly
Removed from the Body?

• Hair root with follicular tissue (root sheath
  cells) attached to it is indicative of hair that
  has been pulled out either by another person or
  by brushing or combing. The rate at which hair
  was removed does affect the tissue adherence.

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Are Efforts Being Made To Individualize Human
Hair?

• Hair can be linked to a particular individual by
  characterizing the nuclear DNA present in the
  hair root or in the follicular tag (best in
  anagen phase).
• If nuclear DNA identification is not possible,
  the criminalists can employ mitochondrial DNA
  analysis (usually highly successful if hair
  length is in the range of at least 1 to 2 cm).
• Mitochondrial DNA DNA found outside the nucleus
  in mitochondria. Maternally inherited.

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Can DNA Individualize A Human Hair?

• Not technically.
• But, it can help exclude a significant portion of
  a population as potential contributors of a hair
  sample.

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Collection And Preservation Of Hair Evidence

• Collected evidence samples must be submitted to
  forensic laboratory for examination accompanied
  by an adequate number of standard/reference
  samples from the victim of the crime as well as
  the suspects.
• Victim This is usually done during the autopsy.
• Suspects May require a court order.

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Famous Hair Cases

• Central Park Jogger
• Ennis Cosby
• See pgs 201 204

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Types of Fibers

• Fibers may become important evidence in incidents
  that involve personal contact.
• Ex homicide, breaking and entering, assault,
  hit and run, sexual assault
• Great care should be taken in the collection of
  fiber evidence to avoid cross-contamination of
  evidence.

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Fiber Categories

• Fibers are classified into 2 broad categories
• Natural
• Man-made

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Natural Fibers

• Fibers derived entirely from animal or plant
  sources.
• Examples include hair coverings from sheep
  (wool), goats (mohair, cashmere), camels, llamas,
  alpacas, mink, rabbit, beaver, and muskrat.
• The most prevalent plant fiber is cotton.
• Cotton fiber shows a microscopic ribbon like
  shape with twists at irregular intervals.

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Man-Made (Synthetic) Fibers

• Fibers derived from either natural or synthetic
  polymers
• These fibers are typically made by forcing the
  polymeric material through the holes of a
  spinneret.
• The first man-made fiber was rayon (regenerated
  fiber made from natural raw materials)
• Synthetic fibers nylon, polyester, and acrylic

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Polymers

• Polymer basic chemical substance of all
  synthetic fibers.
• Substances made from polymers include plastics,
  paints, adhesives, and synthetic rubber
• Starch and cellulose are natural carbohydrate
  polymers

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Fibers

• When comparing two fibers, the following
• properties should be examined
• Color
• Diameter
• Birefringence
• Presence or absence of delustering particles

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Jig Saw Evidence

• It is a virtual certainty that two fabrics share
  a common origin if their fibers can be fitted
  together at their torn edges.

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Forensic Examination of Paint

• Paint most frequently encountered physical
  evidence in hit and run and burglary cases.

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Paint Composition

• Consists of
• A binder
• A solvent
• Pigments

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Paint

• The polymeric make-up of paint binders can
  readily be compared by pyrolysis gas
  chromatography and IR spectrophotometry.

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Paint

• Paint chips may be individualized to a single
  source by examining their color and layer
  structure.
• The color-layer sequence imparts paint with its
  most distinctive forensic characteristics.

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4 Coatings of Auto Finishing

• The automobile finishing system for steel usually
  consists of at least 4 organic coatings
• 1. Electrocoat Primer first layer applied
  to the steel body
• provides corrosion resistance
• - color ranges from black to gray
• 2. Primer Surfacer used to completely smooth
  out and hide any
• seams or imperfections
• - highly pigmented layer
• 3. Basecoat layer used to provide color
  and aesthetics of the
• finish (eye-appeal)
• 4. Clearcoat unpigmented layer used to
  improve gloss, durability
• and appearance.
• - helps resist UV radiation and acid rain

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Paint Data Query

• The PDQ allows an analyst to obtain information
  on paints related to the following
• automobile make
• model
• year