Hairs, Fibers and Paint Chapter 8

1
Hairs, Fibers and PaintChapter 8

• Hair Characteristics
• Fiber Characteristics
• Regenerated Fibers
• Paint Chips- color layer
• Automobile finishes

2
Identification and Comparison of Hair
Good

• Hair can NOT be individualized through its trace
  elemental composition. To combat this PCR is used
• Racial origin can NOT always be determined
  however, significant characteristics do exist
  Ethnic Difference
• Body area can be determined
• Must have a collection of reference standards to
  increase degree of probability
• Significant error rates associated with
  microscopic comparisons, DNA must be confirmed
• Sex can be identified
• In comparing hair, color, length diameter
• Hair is best identified by examining the medulla
  cuticle

Bad
3
Morphology of Hair

• Cuticle- contain scales on exterior of hair shaft
  (keratinized)
• Cortex- main body of shaft, contains pigment
  granules, shape
• Medulla- is either absent or 1/3 the diameter of
  the shaft other animals are ½ or greater
  continuous, interrupted, segmented or absent
• Cuticle and Medulla are best used to distinguish
  if the sample is human or animal

4
Hair is Class Evidence

• Can often determine body area of origin and
  sex
• Can often determine racial origin
• Negroid kinky with dense uneven pigment flat
  to oval in shapeCaucasian straight or wavy
  fairly evenly distributed pigment oval to
  round shape

5
Characteristics of Fibers
poly means many
mer means unit

• Characteristics
• Color, diameter, birefringence, shape, presence
  or absence of delustering particles (usually
  titanium dioxide)
• Rayon
• is classified as regenerated fiber (derived from
  natural material-cellulose)
• First man-made fiber 1911

Forensic Fiber Examination Guidelines
6
Paint Chips
Paint Chips

• Paint chips- individualized to a single source by
  examining color and layer structure
• Pyrolysis gas chromatography- compares the
  polymeric make-up of paint binders
• Automobile finishes- contain an electrocoat,
  primers, colorcoat and clearcoat

7
Describe the proper collection and preservation
of paint evidence from an automobile suspected of
being involved in hit-and-run incident. Paint
that is foreign to the suspect automobile is
observed on the hood.

• Scrape the foreign paint as well as all
  underlying layers of paint off the cars surface
  using a clean knife or scalpel. The scraping
  must clearly show the layer structure of the
  paint.
• Obtain a control paint sample from an adjacent
  undamaged area of the car. Again, all layers
  must be included.
• Package each paint specimen separately in a
  proper container. A druggist fold or a vial
  makes an excellent container.
• Label all specimen containers. Evidence
  collectors name or initials, the date, and the
  sampling location are to be shown. All items
  collected are to be described in the evidence
  collectors field notes.