Forensic Trace Evidence Notes

TRACE EVIDENCE

  • Fragments of physical evidence such as hair, fibers, glass. These items can be transferred when two objects contact each other.

COLLECTING TRACE EVIDENCE

  • Proper PPE (Personal Protective Equipment) should be used.
  • Use single-source tweezers for each item collected to avoid contamination.
  • Collect items in a bindle or envelope.

HAIR AS EVIDENCE

  • Two parts of hair:

    • Root
    • Shaft

  • Hair Structure:

    • Arrector pili muscle
    • Hair shaft
    • Cuticle
    • Cortex
    • Medulla
    • Connective tissue sheath
    • External root sheath
    • Internal root sheath
    • Follicle wall
    • Sebaceous gland
    • Bulge
    • Hair bulb
    • Matrix
    • Dermal papilla
    • Melanocytes
    • Capillary

THREE LAYERS OF THE SHAFT

  • MEDULLA: Contains Mitochondrial DNA
  • CORTEX: Holds the pigment of the hair, giving it color.
  • CUTICLE: Layer that coats the hair, providing protection.

HAIR PHASES OF GROWTH

  • ANAGEN: The growth phase, when the hair follicle produces a hair shaft. Can last for several years.

  • CATAGEN: The transition phase, when the hair follicle begins to regress. Lasts a few weeks.

  • TELOGEN: Resting phase, hair follicle is inactive and sheds. Can last about 3 months.

  • Different types of hair have different growth rates and resting phases.

    • Scalp hair grows faster than pubic hair, which has a strong resting phase.
    • Beard hair is thicker but grows slower.

  • Hair loss that deviates from normal physiology can result in conditions like:

    • ALOPECIA
    • TELOGEN EFFLUVIUM

HUMAN HAIR VS ANIMAL HAIR

  • Forensic scientists compare human hair to animal hair (e.g., dog, deer, rabbit, cat, mouse) for identification purposes.

FORM OF SCALE MARGINS

  • Different forms of scale margins:
    • Smooth
    • Crenate
    • Rippled
    • Scalloped
    • Dentate

DISTANCE BETWEEN SCALE MARGINS

  • Distance between scale margins:
    • Distant
    • Near
    • Close

SCALE PATTERNS

  • Scale Patterns:
    • Simple Coronal
    • Diamond Petal (Narrow and Broad)
    • Regular Mosaic
    • Flattened Irregular Mosaic
    • Regular Wave
    • Irregular Wave
    • Single Chevron
    • Double Chevron
    • Streaked
    • Transitional

FIBER EVIDENCE

  • Natural Fibers:

    • PLANT: Cotton, Flax, Jute, Hemp, Coconut, Sisal
    • ANIMAL: Wool, Silk, Cashmere, Mohair, Alpaca, Angora
    • MINERAL: Asbestos

  • Synthetic Fibers:

    • Polyester
    • PVC
    • Nylon
    • Rayon
    • Acrylic
    • Lycra

FIBER AS EVIDENCE

  • Can be transferred from person to person or place to place.
  • Can be used to show physical contact was made.
  • Types of crimes where fiber analysis is valuable: Assault, Homicide, Rape, Burglary, Hit-and-Run.

EXAMPLES OF FIBERS

  • Coarse Wool
  • Fine Wool
  • Alpaca
  • Cashmere
  • Silk
  • Linen
  • Cotton
  • Polyester

COMPARING FIBERS

  • Physical Characteristics:
    • Color
    • Diameter
    • Fiber Class

TOOLS USED FOR COMPARISON

  • Stereomicroscopes
  • Comparison Microscopes
  • Compound Microscopes with Polarized Light
  • Gas Chromatography
  • Thin Layer Chromatography

GLASS AS EVIDENCE

  • Glass is produced in a wide variety of forms and compositions, affecting its properties.

  • Glass is the inorganic product of fusion which has cooled to a rigid condition without crystallizing.

  • When glass breaks, fragments can be ejected in different directions. Fragments have been found up to 4 meters from the object.

  • The closer an object is to the breaking glass, the more likely it will have fragments on it.

  • The person breaking the glass will have more fragments on them.

GLASS ANALYSIS

  • Usually a comparison of two or more glass fragments in an attempt to determine if they originated from a different source or to determine if the fragment is actually glass.

PAINT AS EVIDENCE

  • Evidence that is transferred from a main source to the scene of a crime.
  • Paint is a liquefiable mixture of organic and inorganic substances (pigments, resins, solvents, additives, fillers) that converts to a solid film after application.
  • Chemical compounds are analyzed.