Notes on Visual Identification of Hair and Fiber Evidence

Introduction

• Focus on basics of visual identification of hair and fiber evidence.
• Use of ProScope HR digital microscope for microscopic analysis.
• Equipment commonly used by forensic scientists.

Differences Between Hairs and Fibers

• Fibers:
  • Shapes can be uniform or irregular.
  • Synthetic fibers: uniform shape.
  • Natural fibers: irregular shape.
• Hairs:
  • Always irregular due to natural cell structures.
  • Circular shape.
  • Structural features: cuticle and medulla (absent in fibers).

Information from Hair and Fiber Evidence

• Fibers:
  • Can determine if fiber is natural or synthetic.
  • Synthetic fibers are man-made.
  • Class evidence: cannot be linked to a specific source.
• Hairs:
  • Determine human vs non-human.
  • Species identification via cuticle pattern.
  • Human hair: assess ancestry, body origin, length, dye treatment.
  • Root presence: natural shed vs forcibly removed, DNA analysis possible.

Microscopic Analysis of Hair

• Structural Features:
  • Cuticle and medulla visible under a microscope.
  • Cuticle: outer layer with overlapping scales.
  • Medulla: canal-like structure through hair center.
• Cuticle Patterns:
  • Coronal: stacked paper cups, common in rodents/bats.
  • Spinous: flower petals, seen in cats.
  • Imbricate: narrow scales, in humans and dogs.
• Medullary Index:
  • Ratio of medulla thickness to overall hair thickness.
  • Human medulla: thinner.
  • Animal medulla: thicker.

Microscopic Analysis of Fibers

• Categories:
  • Natural: animal hairs, vegetable fibers (plants), mineral fibers.
  • Synthetic: organic fibers (polymers), inorganic fibers (fiberglass).
• Natural Fibers:
  • Irregular shapes.
  • Plant fibers: highly irregular and twisted (e.g., cotton).
• Synthetic Fibers:
  • Uniform characteristics, three main shapes: trilobal, hollow, circular.
  • Example: polyester (circular), acrylic (dog bone shape).

Conclusion

• Hairs and fibers can be distinguished by shape, structural features, uniformity or irregularity.
• Ability to differentiate based on microscopic features and analysis.