Transcript Chapter 10 Trace Evidence: Hairs and Fibers

Chapter 10
Trace Evidence: Hairs and
Fibers
1.
2.
3.
4.
5.
6.
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Objectives:
Describe the cuticle, cortex, and medulla of hair.
Describe the three phases of hair growth.
Explain the distinction between animal and
human hairs.
List hair features that are useful for the
microscopic comparison of human hairs.
Explain the proper collection of hair evidence.
Describe the role of DNA typing in hair
comparisons.
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Morphology of Hair
skin appendage
hair follicle
cuticle
cortex
medulla
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2
Cuticle
outer covering
overlapping scales
keratinized cells
distinguish human from animal
cast in enamel/vinyl
scale patterns used to identify
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Medulla
central canal
narrow in human
wide in animals
patterns used to id animals
Sample Animal Hairs
multiserial
ladder
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uniserial
ladder
lattice
vacuole
fragmented
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continuous
interrupted
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Cortex
between cuticle and medulla
contains pigment
color shape distribution
contains fusi (air pockets)
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Growth Stages
root
anagen (lasts 6 years)
active growing follicle makes hair
follicular tag
rich in DNA
catagen (2-3 weeks)
root elongated
transition phase
telogen (2-6 months)
root club shaped
shaft pushed out (shed)
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Human/Animal Hair Comparison
root bulbous
banding
artificial dyes
medulla narrow
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root varies
spade (dog)
frayed (cat)
wine glass (deer)
natural banding
medulla wide
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Human Race Comparison
Caucasian
dia: moderate
pig: sparse moderately dense
XS: oval
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Negroid
fine–moderate
dense &
clumped
flattened
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Asian
coarse
dense-patches
round w/thick
cuticle
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Human Hair Color Comparison
based on pigment distribution
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Head/Pubic Hair Comparison
head – straight shaft
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pubic – “twists” in shaft
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FBI Hair Comparison Papers
Scientific Paper
Second Paper
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Chapter 10
Trace Evidence: Hairs and
Fibers
1.
2.
3.
4.
7/17/2015
Objectives:
Classify fibers.
Describe the structure of a
polymer.
List the properties of fibers that are
most useful for forensic
comparisons.
Describe the proper collection of
fiber evidence.
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Is the second most common type of trace evidence
Fiber Evidence
Individual
Fibers
Viewpoints
Fabric
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Threads
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Fiber Evidence Classifications
Fiber Classifications
Natural Fibers
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Manufactured Fibers
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Natural Fiber Classifications
Natural Fibers
Mineral
Plant
Animal
Learn more details about the types of fibers at the
following link http://www.teonline.com/fiberhistory.html
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Mineral Fibers
Asbestos
Insulation
 Fire retardant

Fiberglass
Filters
 Insulation

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Plant Fibers
Cotton


Too common
Little significance
Kapok


Flotation devices
Very buoyant
Flax


Linen
Bamboo shaft like
Hemp
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
Large diameter
Cords and ropes
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Animal Fibers
Wool


Sheep hair
Coarse, irregular
Cashmere


Goat hair
Smooth
Camel

Fine diameter
Silk
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
Secretion of insect
Small diameter
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Manufactured Fiber Classifications
Manufactured Fibers
Regenerated
Synthetic
natural materials
digested
reconstituted
polymer
macromolecules
monomers
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Regenerated Manufactured Fibers
Acetate (Celanese)

Cellulose acetate
•
•
•
•
luxurious
soft
fast drying
shrink, moth, mildew resistant
Rayon

Cellulose fibers
• highly absorbent
• soft
• easily dyed
Triacetate



shrink, wrinkle resistant
washable
maintains creases and pleats well
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Synthetic Manufactured Fibers
Acrylic

fluoresce in UV
• warm
• wool like
• moth, oil, chemical, sunlight
resistant
Aramid (Kevlar)

heat resistant strong fibers
• does not melt (500°C)
• flame, stretch resistant
• strength for weight
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Synthetic Manufactured Fibers
(con’t.)
Nylon

polyamide (peptide bonds)
•
•
•
•
strong
lustrous
washable
resilient
Olefin

polypropylene, polyethylene
• wicks moisture
• quick drying
• soil, mildew, perspiration, rot, weather
resistant
• strong/lightweight
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Synthetic Manufactured Fibers
(con’t.)
Polyester

Dacron (ester bonds)
•
•
•
•
•
strong
stretch, shrink, chemical, wrinkle resistant
retains heat set pleats/creases
washable
quick drying
Spandex

Polyether polyols
•
•
•
•
•
can stretch 500% without breaking
returns to original shape
light weight
stronger than rubber
resistant to body oils
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Fiber Identification and Comparison
Microscopic Examination
striations, pitting may be characteristic of fibers
 cross section shape

Chemical Composition

textile chemists have test to help classify polymer types
Birefringence (refractive indices)

polymers are crystalline – see table p 376
Infrared Absorption

absorption spectra can be used to identify generic class
of fiber
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Collection and Preservation of
Fiber Evidence
most fiber evidence not visible to naked eye
 need
to preserve “carriers” of fiber evidence
• carefully package clothing in paper bags
• don’t package from same surface
• fold to protect suspected areas
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References
Houck, Max M. “Forensic Hair
Comparisons.” Forensic Business
Research and Development for College of
Business and Economics of West Virginia
University
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