Forensic Analysis of Hair

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Forensic Analysis of Hair

• Alex Picariello
• SBF6-02
• Instructor Mary Villani

2
Hair in Forensics

• It is important to note that it is impossible for
  experts to individualize a hair (in other words,
  match it perfectly to any single head/body)
• Hair samples can be used to place an individual
  at a location by comparing hair recovered from
  the crime scene with control samples

3
Hair Morphology

• Hairs grow from hair follicles
• The bulb (root) of the hair is contained within
  the follicle
• The shaft of the hair connects with the root
• The shaft has three parts the cuticle, the
  cortex, and the medulla
• The shaft ends with the tip of the hair

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The Cuticle

• Outside layer of the hair
• Allows the hair to retain structural features and
  resist chemical decomposition
• Formed by layered scales (hardened and flattened
  specialized cells that come from the follicle)

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The Cuticle (Continued)

• Scale pattern is useful for species
  identification of hair samples
• Observing the scale pattern is done by creating a
  cast (embed the hair in a softened vinyl or nail
  polish and then remove it once the medium hardens)

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The Cortex

• Layer underneath the cuticle
• Composed of spindle-shaped cells that run
  parallel to the hair
• Contains the pigment granules that give hair its
  color (distribution, color, and shape of these
  granules help with comparing hair samples)

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The Medulla

• Appears to be a central canal running the
  length of the hair
• Medullary Index The fractional value that
  demonstrates the diameter of the medulla in
  relation to the diameter of the entire hair shaft
  (animals have an MI of 1/2 or greater, humans 1/3
  or less)
• The shape of the medulla changes from animal to
  animal (humans have cylindrical medullae, if they
  are present at all, whereas cats have
  scaly-looking medullae)

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The Medulla (Continued)

• Medullae can appear in three forms fragmented,
  continuous, interrupted, or absent
• The three forms vary from person to person, and
  even from hair to hair on a single individual

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Hair Roots

• The hair root allows for the growth of the hair
• There are three phases of root development
  Anagen, Catagen, and Telogen
• Each root phase has a different shape and size

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• Root Development

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Anagen Phase

• Can last up to 6 years, during which time hair
  growth occurs
• The root is connected to the follicle and looks
  like a flame
• Forcibly removed roots in the Anagen phase may
  have a piece of DNA attached known as a
  follicular tag (useful for individualization)

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Catagen Phase

• Can last 2-3 weeks, hairs grows at a slower rate
• Elongated appearance as the root is gradually
  being forced out of the hair follicle

13
Telogen Phase

• Can last 2-6 months, during which time hair
  growth has completely stopped
• Hair is eventually forced out of the follicle and
  shed naturally

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Hair Identification

• It is important for forensic experts to be able
  to figure out to which species a particular hair
  sample belongs (this can be done by looking at
  the scale formation of the cuticle and the
  medullary index)
• The most important characteristics of hair are
  scale structure, medullary index, and medullary
  shape
• Forensic experts are often requested to match
  crime scene hairs with hairs removed from a
  suspect

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Hair Identification
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Hair Comparison

• Criminalists attempt to match the color, length,
  and diameter of the hair
• Presence of medullae, and the pigment granules
  shape, size, and distribution are important
  comparable characteristics

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Determining Body Area
-The location on the body of hair found at a
crime scene can be determined by noting key
characteristics
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Determining Race

• Negroid Hair
• Kinky
• Dense, unevenly-distributed pigments
• Flat to oval cross-section

• Caucasoid Hair
• Straight or wavy
• Fine to coarse, evenly-distributed pigments
• Oval to round cross-section

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Race Hairs
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Determining Forced Removal

• Hair that fall naturally from the body will have
  a bulbous root
• Hairs that have root sheath cells (the follicular
  tissue) attached are more likely to have been
  forcibly removed

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Individualizing Hair

• Forensic experts can use the DNA found in the
  root or in the follicular tissue attached to the
  root for individualization
• The follicular tag is the best source of DNA
• DNA is best found in the Anagen and Catagen phases

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Collecting Hair Samples

• Control samples must contain a large quantity of
  hair (roughly 50 hairs) from that particular body
  area, because individual hairs can vary on a
  single person

• When collecting control samples from suspects, it
  is important to obtain hairs from the same part
  of the body that the crime scene hairs came from
• The entire length of the hair should be collected
  because a hair can vary morphologically over its
  entire length

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Collection
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References

• http//www.fbi.gov/hq/lab/fsc/backissu/july2000/de
  edric1.htmHair20Evidence
• http//www.crimeandclues.com/hair_evidence.htm
• http//www.crimelibrary.com/criminal_mind/forensic
  s/trace/5.html
• http//www.dermatology.org.uk/portal/activities/im
  ages/hair-follicle-parts.jpg
• http//thebeautybrains.com/wp-content/uploads/2006
  /10/damagedhairshaft.jpg

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References (Continued)

• http//www.top-hair-loss-remedy.com/images/hair-cr
  oss-section.gif
• http//hairmedulla.com/assets/img/HairMedulla.jpg
• http//www.fbi.gov/hq/lab/fsc/backissu/july2004/im
  ages/2004_03/figure22.jpg
• http//www.dermatology.org.my/hairloss/images/hair
  loss/catagen.jpg