Summary of Hair Analysis- Lesson 2 (Forensics)

Summary of "Hair Analysis - Lesson 2 (Forensics)"

This video lesson continues the forensic study of Hair Analysis, building upon concepts introduced in Lesson 1. It focuses on the forensic significance of hair, its structure, differences between human and animal hair, and introduces the Medullary Index as a key analytical tool. The lesson also touches on advanced chemical testing methods used in forensic investigations.

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Main Ideas and Concepts

• Recap of Lesson 1: Hair as Evidence
  • Hair can be class evidence or individual evidence:
    • Individual evidence if the hair contains the follicle (root) with nuclear DNA.
    • Class evidence if no follicle is present, relying on microscopic/macroscopic features for analysis.
  • Hair has two main parts:
    • Follicle (root): Contains nuclear DNA.
    • Shaft: Composed of three layers:
      • Cuticle: Outer protective layer with scales.
      • Cortex: Middle layer containing pigment.
      • Medulla: Central core.
• Macroscopic vs Microscopic Properties
  • Macroscopic properties: Visible without a microscope (color, texture, length).
  • Microscopic properties: Require a microscope (medulla pattern, cuticle condition, Medullary Index).
• Hair Variation
  • Hair varies by body region (head, eyebrows, beard, pubic, underarm, etc.).
  • Hair varies between humans and animals.
  • Different ethnic groups have distinct hair characteristics (e.g., strand count, texture, pigmentation).
• Human vs Animal Hair Differences
  • Pigmentation: Human hair color is generally consistent along the shaft; animal hair may show abrupt changes.
  • Medulla:
    • Human hair medulla is thin, about one-third of the hair shaft diameter.
    • Animal hair medulla is wide and well-defined.
  • Cuticle scale patterns differ between humans and animals.
• Medullary Index
  • Defined as the ratio of the medulla diameter to the total hair diameter.
  • Formula:
    Medullary Index = Width of Medulla / Diameter of Hair
  • Interpretation:
    • ≥ 0.5 → Likely animal hair.
    • ≤ 0.33 → Likely human hair.
    • Between 0.33 and 0.5 → Indeterminate; requires judgment.
  • Example calculation:
    • Hair diameter = 110 microns
    • Medulla width = 58 microns
    • Medullary Index = 58 / 110 = 0.53 → likely animal hair.
• Hair Composition and Strength
  • Hair is made of Keratin, a strong protein formed by amino acid chains in a helix.
  • Keratin’s structure makes hair resistant to decomposition, useful for forensic analysis even after long postmortem intervals.
• Hair Collection and Analysis
  • Hair can be collected by plucking, shaking, scraping, or using adhesives.
  • Microscopic examination is essential; electron microscopes provide magnification up to 50,000x.
  • Chemical testing can also analyze hair composition.
• Forensic Applications of Hair Analysis
  • Hair can incorporate substances ingested or absorbed, allowing toxicology timelines.
  • Example: The Napoleon Bonaparte case:
    • Neutron Activation Analysis (NAA) was used to detect arsenic in his hair decades after death.
    • NAA involves exposing hair to neutron beams to detect trace elements.
    • This test helped support theories that Napoleon was poisoned rather than dying of stomach cancer.

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Methodology / Instructions

• Medullary Index Calculation
  1. Measure the width of the medulla.
  2. Measure the diameter of the entire hair.
  3. Divide the medulla width by the hair diameter.
  4. Interpret the ratio:
     • ≥ 0.5 → Animal hair.
     • ≤ 0.33 → Human hair.
     • Between 0.33 and 0.5 → Use best judgment.
• Hair Collection Techniques
  • Plucking
  • Shaking
  • Scraping
  • Using adhesives on surfaces or victims/objects
• Microscopic Analysis
  • Use light microscopes for general microscopic properties.
  • Use electron microscopes for highly detailed images.
• Chemical Testing
  • Neutron Activation Analysis to detect trace elements and toxins in hair samples.

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Speakers / Sources Featured

• Primary Speaker: The forensic instructor/lecturer presenting the lesson (unnamed).
• Referenced Case: Hair analysts involved in the Casey Anthony trial (mentioned as a research suggestion).
• Historical Example: Forensic scientists who performed Neutron Activation Analysis on Napoleon Bonaparte’s hair.

Category

Educational

Video