1 forensic trichology sfs1. students will recognize and classify various types of evidence in...
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FORENSIC TRICHOLOGY
SFS1. Students will recognize and classify various types of evidence in relation to the definition and scope of Forensic Science b. Distinguish and categorize physical and trace evidence
(e.g. … hair)
SFS2. Students will use various scientific techniques to analyze physical and trace evidence. b. Analyze the morphology and types of hair.
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ESSENTIAL QUESTIONS
How can you distinguish the types and layers of hair?
How can you distinguish animal and human hair?
How can you distinguish the growth periods of hair?
How can you distinguish one human hair from another?
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HISTORY
1590 – First operating compound microscope
1847 – Earliest examination of hairs in criminal investigation
1861 – First forensic investigation of human hair comparison of hair found on victim to those of defendant
1906 – Documented use of hair in forensic investigations to determine identity
1910 – Microscopic studies of both human and animal hair
1951 – Use of adhesive tape to collect trace evidence
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TYPES OF HAIRS
Primordial hairs – develop from 9 to 22 wks.
Lanugo hairs – fetal body hair shed by 36-40 wks.
Vellus hairs – “peach fuzz” pre-pubescent hair
Terminal hairs – adult hair stimulated to grow by androgens (male hormones)
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HAIR STRUCTURE
Hair is primarily composed of the protein keratin and the pigment melanin
Hair is both living and dead – the living part (root) is enclosed within the follicle, while the dead part is the shaft
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HAIR STRUCTURE
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Cross-Section of a Hair
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HAIR STRUCTURE
Cuticle - a translucent outer layer of the hair shaft consisting of scales that cover the shaft. Cuticular scales always point from the proximal (root) end of the hair to the distal (tip) end of the hair.Not useful in individualizing human hair,
but can be used for species identification
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HAIR STRUCTURE
Cuticle Structure
1. Coronal “crown-like”
Rare in humans
Typical of rodents.
Found in hairs of very fine diameter.
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HAIR STRUCTURE
Cuticle Structure
2. Spinous “petal-like.”
Never found in humans.
Common in cats, seals, and minks.
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HAIR STRUCTURE
Cuticle Structure
3. Imbricate “flattened”
Common in humans
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HAIR STRUCTURE
Cortex - is the main body of the hairEmbedded with pigment granules that
give hair its colorThe color, shape and distribution of the
granules provide points for forensic comparison
Dyed hair has uniform pigmentation in cortex and cuticle
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HAIR STRUCTURE
In humans, pigment granules are commonly distributed toward the cuticle, except in red-haired individuals.
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HAIR STRUCTURE
Animal hairs have the pigment granules commonly distributed toward the medulla.
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HAIR STRUCTURE
Medulla - a cellular column running through the center of the cortex
Presence of medulla varies quite a bit: even hair to hair
Useful in distinguishing among animal speciesMEDULLARY INDEX = diameter of the medulla
diameter of the hair shaft
Humans: medullary index < 1/3
Animals: medullary index > 1/2
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Medulla Structure (Animal)
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HAIR STRUCTURE
Medullary Patterns
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Medulla Structure (Human)
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GROWTH AND REPLACEMENT OF HAIR
Mammalian hair follicles go through three distinct growth cycles.
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GROWTH AND REPLACEMENT OF HAIR
Anagen: the active growth phaseScalp hairs spend 2-7 yrs in this phase and
grow approximately 1 cm/mo.Up to 90% of the hairs are in this growth
cycle Follicle is attached to the root by the
papilla. The hair must be pulled to be lost.
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GROWTH AND REPLACEMENT OF HAIR
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GROWTH AND REPLACEMENT OF HAIR
Catagen: the transitional stageLasts two to four weeksOnly 2% of the hairs are in this phaseFollicle is losing blood supply and hair is
retreating to the surface
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GROWTH AND REPLACEMENT OF HAIR
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GROWTH AND REPLACEMENT OF HAIR
Telogen: the resting phaseLasts two to four months, until hairs fall
out naturally or are forcibly removedAbout 10% to 18% of the hairs are in
this phase
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GROWTH AND REPLACEMENT OF HAIR
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IDENTIFICATION OF HUMAN HAIR
The first step of forensic identification and comparison of hairs begins with whole mount light microscopy.
The hair(s) in question must be identified as to species, race and body (somatic) origin.
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IDENTIFICATION OF HUMAN HAIR
Human hairs can be readily distinguished from animal hairs in primarily by examining the cuticles and medullae.
Individualizing human hairs is done by examining cortex features and by analyzing DNA.
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RACIAL ORIGIN
EuropeanShaft: straight to wavyShaft diameter: moderate with
minimal variationCortex: sparse to moderately
dense with melanin; fairly even distribution
Medulla: variableCross-sectional shape: oval
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EXAMPLES OF RACIAL HAIR
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RACIAL ORIGIN
AfricanShaft: prominent twist and curlShaft diameter: moderate to fine
with considerable variationCortex: melanin is densely
distributed and arranged in prominent clumps
Medulla: fragmented or absentCross-sectional shape: flattened
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EXAMPLES OF RACIAL HAIR
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RACIAL ORIGIN
AsianShaft: straight with thick cuticleShaft diameter: coarse with little
or no variationCortex: densely distributed
melanin and often arranged in large patchy areas or streaks
Medulla: prominent (often broad and continuous)
Cross-sectional shape: round
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EXAMPLES OF RACIAL HAIR
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SOMATIC ORIGIN
Somatic Origin: Head
Long with moderate shaft diameter and diameter variation
Medulla absent to continuous and relatively narrow when compared to the structure of hairs from other body areas
Often with cut or split tipsCan show artificial treatment, solar
bleaching, or mechanical damageSoft texture, pliable
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SOMATIC ORIGIN
Somatic Origin:Pubic
Shaft diameter coarse with wide variations and buckling
Medulla relatively broad and usually continuous when present
Root frequently with tagTip usually tapered, rounded, or
abradedStiff texture, wiry
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SOMATIC ORIGIN
Somatic Origin:Limb hairs (arm or leg)
Diameter fine with little variationGross appearance of hair is arc-like in
shapeMedulla is discontinuous to trace with a
granular appearanceTips usually tapered often blunt and
abraded, rounded scale ends due to wear
Soft texture
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SOMATIC ORIGIN
Somatic OriginBeard or Mustache hairs
Diameter very coarse with irregular or triangular cross-sectional shape
Medulla very broad and continuous, may be doubled
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IDENTIFICATION OF HUMAN HAIR
Somatic OriginChest hairs
Shaft diameter moderate and variableTip often darker in color, long and fine, arc-
likeMedulla may be granularStiff texture
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IDENTIFICATION OF HUMAN HAIR
Somatic OriginUnderarm hairs
Resemble pubic hairs in general appearance, but less wiry
Medullar appearance similar to limb hairsDiameter moderate and variable with less
buckling than pubic hairsTips long and fine, frequently with bleached
appearance
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IDENTIFICATION OF HUMAN HAIR
Somatic Origin:Other
Eyebrow: Stubby, some diameter fluctuation, saber-like in appearance
Eyelash: Short, stubby with little shaft diameter fluctuation, saber-like in appearance
Trunk: A combination of features of limb and pubic hairs, a transitional hair
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IDENTIFICATION OF HUMAN HAIR
As a rule, most forensic comparisons are conducted using scalp or pubic hairs. Body and limb hairs are generally considered unsuitable for comparison purposes.
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VARIATIONS IN COLOR
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COLLECTION AND EXAMINATION OF HAIR
Always photograph the item and note its location first before collecting it.
Always be sensitive to cross-contamination issues.
Always wear gloves to collect evidence.
Always use clean, unused paper bindles or containers.
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COLLECTION AND EXAMINATION OF HAIR
Use fingers or tweezers to collect crime scene evidence.
Collect good representative exemplary (known) hairs from the scalp and/or pubic region.
Collect exemplars from both the victim and suspect.
Always maintain the chain of custody.
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COMPARATIVE MICROSCOPY
Skillful microscopic technique provides the forensic hair examiner with a highly discriminating means to examine and compare hair, and utilizes various types of microscopes.
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COMPARATIVE MICROSCOPY
Stereomicroscope - permits gross observations of the hairs; allows a rapid overview of the range of characteristics.
Polarizing microscope - delineates the hair’s finer structural characteristics.
Transmitted light microscope - allows a side-by-side comparison of the known and questioned hairs. Hairs are compared from their root end to their tip end.
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CONCLUSION AND REPORT WRITING
Forensic laboratory reports of hair comparisons normally will provide one of three answers: The hairs matched in microscopic
characteristics, indicating an association. The hairs are not alike and therefore did not
come from the same person. No conclusion can be drawn from the evidence.
This may be due to insufficient specimen, racial mixtures, or unsuitable exemplars.
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DNA Analysis
Nuclear DNACombination of both parentsHair root/follicle
Mitochondrial DNAMother’s lineage onlyHair shaft