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Hair as Evidence

Hair as Evidence. Form & Structure of Hair. Hair as Evidence. Hair is frequently found at a crime scene Locard Exchange Principle Hair is considered class evidence Could possibly be individualized if root tissue is still attached to the hair

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Hair as Evidence

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  1. Hair as Evidence Form & Structure of Hair

  2. Hair as Evidence • Hair is frequently found at a crime scene • Locard Exchange Principle • Hair is considered class evidence • Could possibly be individualized if root tissue is still attached to the hair • Very useful in supporting circumstantial evidence • Can be used to place someone at the crime scene • Can link a criminal with the crime

  3. Hair as Evidence • From hair, one can determine: • If the source is human or animal • Race • Sometimes • Based on shape of hair • Origin of the location on the source’s body • Whether the hair was forcibly removed • By whether or not root attached • Whether the hair has been treated with chemicals • If drugs have been ingested

  4. Interesting Hair Facts • Human body has about 5 million hairs • Most are downy hair covering body • Hair is continuously shed & renewed throughout lifetime • About 100/24 hour period on head alone • Much higher rate of loss for body hair • Hair on the head • Blonds have most – about 120,000 strands • Redheads have least – about 80,000 strands • Black/Brown in the middle – about 100,000 strands

  5. Hair Morphology • Must understand structure of hair to analyze it • Made up of cross-linked protein polymers • Very resistant to breaking down • Grows from a tube-like organ called a follicle • Located in the dermis

  6. Hair Morphology • Follicle is linked to the body’s blood supply • Whatever is taken into body is distributed to part of hair growing at that time • Important in analyzing hair for drugs & poisons • Hair shaft extends through epidermis & ends at tip • Shaft composed of dead cells

  7. Hair Shaft • Composed of three parts: • Cuticle • Clear, outer covering of shaft • Made of tough, overlapping scales • Scales finer in humans compared to animals • Cortex • Made of protein called keratin • Embedded with pigment that gives hair color • Contains air sacs called cortical fusi • Different shapes & sizes • Possible class characteristic • Medulla • Canal running down center of cortex • May be dark or translucent depending on contents

  8. The Cuticle • Outer most layer of hair covered with scales • Scales point toward tip of the hair • Scales differ among species of animals • Named based on their appearance • Three basic scale patterns include: • Coronal • Mouse • Spinous • Cat • Imbricate • Human

  9. Human Scales To visualize scales: • Paint clear fingernail polish on a glass slide. • When the polish begins to dry, place a hair on the polish. • When it is almost dry, lift off the hair and observe the scale imprints. • What pattern is seen in this slide?

  10. The Cortex • Gives hair its shape • Has two major characteristics: • Melanin is pigment that gives hair its color • Produced by melanocytes located in the follicle • Cortical fusi are air spaces usually found near the root • Sometimes found throughout the cortex

  11. The Medulla • May be dark or translucent • Depends on whether it contains air, liquid, or pigment • May be continuous, interrupted, or fragmented • Human hair usually lack a medulla or has one that is fragmented • Except for Native Americans & Asians whose hair have a continuous medulla • Animal hairs have wide variety of medullar patterns • Patterns can identify some species

  12. The Medulla • Hair’s core that is not always visible • Comes in different types and pattern • Patterns Include: • Interrupted • Fragmented • Continuous • Stacked • Absent

  13. Human Medulla Human medulla may be continuous, fragmented, or absent

  14. Medullary Index • Determined by measuring the diameter of the medulla then dividing it by the diameter of the hair • MI = medulla diameter x 100 hair diameter • Medullary index for human hair is generally <33 • Medullary index for animal hair is generally >50

  15. Medullary Index Human MI = 25 Deer MI = 100 Raccoon MI = 80

  16. Hair Shape • May be straight, curly, or kinky • Depends on the cross-section • Cross-section may be: • Round • Oval • Crescent-shaped: Round (Straight) Oval (Curly) Crescent moon (Kinky)

  17. Hair Shape by Race Undulated • Asians & Native Americans • Round cross section & no twisting • Caucasians, Mexicans, & Middle Eastern heritage • Oval cross section & rarely twist • Evenly distributed pigmentation • African heritage • Crescent-shaped cross section with a twist • Dense, clumped pigmentation Twisted

  18. British CSI School Hair & Fiber Analysis

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