Hair as Trace Evidence (Forensics)

Hair As Trace Evidence (Forensics)

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  • Created by: Nelly
  • Created on: 02-01-12 12:18

Characteristics

Difference due to:

  • Species
  • Somantic Origin
  • Cosmetic Treatment
  • Race
  • Age
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Structure

Cuticle = Outside surface of hair

Cortex = Major part of hair mass

Pigment = contained within cortex - defines colour

Medulla = At centre of shaft, within cortex - normally filled with air and increases hair strength

Distal Terminus = tip of hair

Proximial Terminus = root of hair

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Cuticle

CUTICLE

  • Layer of cells  - outer surface of hair
  • Cells overlap with free ends pointing towards distal terminus

3 types of cuticle

  • Coronal (Crown-like) - rarley human (Rodent, bats, cats)
  • Spinous (petal-like) - NEVER human (Seal, cats other mammals)
  • Imbricate (flattened) - Human (and a few other animmals)
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Medulla

MEDULLA

  • ABSENT
  • CONTINUOUS
  • DISCONTINUOUS

If Medullary Index (MI) less than or equal to 1/3 = human

If MI greater than 1/2 = animal

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TERMINI

DISTAL TERMINUS - can tell how hair was cut and time since last treatment.


PROXIMAL TERMINUS - can tell how hair was shed, naturally or mechanially?

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Cosmetic Treatment

Can change colour, shape and chemistry of hair

Surface Treatment:

  • Shampoo
  • Conditioner
  • Sprays
  • Lotions

Whole Fibre Treatment:

  • Colourants
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Hair as Physical Evidence

Ideal physical evidence: -

  • Significant amounts are lost unwittingly.
  • Hair is chemically quite stable.
  • DNA evidence can be obtained from a single hair providing individualisation of the sample.
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Analysis

Need to determine:

Species - human or animal?

Geographical Origin - Race

Somatic Origin - from where on body?

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Somatic Origin 1

Head Hair

  • Vary in length
  • Tips often cut or split and rarely tapered
  • Diameter varies very little along length

Pubic Hair

  • Shorter, curlier, flatter cross section
  • Continuous medulla

Limb Hair

  • Finer and lighter in colour
  • Slight Pigmentation
  • 3-6mm in length
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Somatic Origin 2

Eyebrows/lashes

  • Short curved with tapared tips
  • Large Medulla
  • Relatively Coarse

Chest Hair

  • Stiff texture
  • Moderate diameter variation
  • Tapered Tips
  • Small Diamete than pubic hairs
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