1. Chapter 10 Trace Evidence: Hairs and Fibers
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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Cuticle
outer covering
overlapping scales
keratinized cells
distinguish human from animal
cast in enamel/vinyl
scale patterns used to identify
Even 4 4/28 ODD 1& 3 4/29
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Medulla
central canal
narrow in human
wide in animals
patterns used to id animals
Sample Animal Hairs
multiserial
ladder
uniserial
ladder
vacuole
lattice
fragmented
continuous
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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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7. Human/Animal Hair Comparison
root bulbous
banding
artificial dyes
medulla narrow
root varies
spade (dog)
frayed (cat)
wine glass (deer)
natural banding
medulla wide
Even 4 Apr 30 ODD 1 and 2 May 1
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Human Race Comparison
Asian
coarse
dense-patches
round w/thick cuticle
Caucasian
dia: moderate
pig: sparse -moderately dense
XS: oval
Negroid
fine–moderate
dense & clumped
flattened
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9. Human Hair Color Comparison
based on pigment distribution
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10. Head/Pubic Hair Comparison
head – straight shaft
pubic – “twists” in shaft
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11. FBI Hair Comparison Papers
Scientific Paper
Second Paper
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12. Chapter 10 Trace Evidence: Hairs and Fibers
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
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14. Fiber Evidence Classifications
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15. Natural Fiber Classifications
Learn more details about the types of fibers at the following link
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Mineral Fibers
Asbestos
Insulation
Fire retardant
Fiberglass
Filters
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Plant Fibers
Cotton
Too common
Little significance
Kapok
Flotation devices
Very buoyant
Flax
Linen
Bamboo shaft like
Hemp
Large diameter
Cords and ropes
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Animal Fibers
Wool
Sheep hair
Coarse, irregular
Cashmere
Goat hair
Smooth
Camel
Fine diameter
Silk
Secretion of insect
Small diameter
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19. Manufactured Fiber Classifications
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20. Regenerated Manufactured Fibers
Acetate (Celanese)
Cellulose acetate
luxurious
soft
fast drying
shrink, moth, mildew resistant
Rayon
Cellulose fibers
highly absorbent
easily dyed
Triacetate
shrink, wrinkle resistant
washable
maintains creases and pleats well
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21. 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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22. 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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23. 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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24. 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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25. 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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