Criminal Mischief: Episode #53: Forensic Science For Crime Writers: Trace Evidence
LISTEN: https://soundcloud.com/authorsontheair/episode-53-trace-evidence
PAST SHOWS: https://www.dplylemd.com/podcasts
SHOW NOTES:
Locard Exchange Principle
Evidence is Class or Individualizing
Evidence is Associative—connects someone to an object, a location, or another person
Types of Trace Evidence
Hair
Structure:
Medulla:
None, Continuous, Interrupted, Fragmented
Humans: None or fragmented
Thickness: Humans 1/3
Cortex: Largest part in humans
Contains pigment
Contains air pockets and ovoid bodies
Cuticle: Like fish scales
Coronal-crown-like—rare in humans
Spinous—petal-like—cats but not humans
Imbricate—flat—found in humans
Race/Sex/Age—difficult/impossible to determine
Site of Origin
Manner of Removal
Chemical Analysis
DNA—Nuclear vs Mitochondrial
Snowball The Cat Case
Shirley Duguay-victim
Douglas Beamish—perpetrator
Fibers
Classification:
Natural: cotton, wool, silk, hemp, etc.
Manufactured: from cotton or wood-Rayon, acetate
Synthetic: polymers—nylon, polyester
Wayne Williams Atlanta Child Killer Case
Examination: diameter/shape/color/shine/crimps/curls’ =
Refractive Index
Birefringence
Glass
Physical Exam: color/thickness/shape/pattern/opacity
Optical: transmit/reflect/refract
Chemical: boron/lead/pigments
Fracture Patterns
Glass Gunshot Fracture Patterns
Paint
Basic Parts: binders/pigments/extenders/modifiers
Cars: Electroplate Primer/Primer/Basecoat/Clear coat
Layers and repainting
Fracture Patterns
Soil/Plants
Place of origin
DNA
LINKS:
Snowball The Cat: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/snowball-cat
Fiber Evidence and the Wayne Williams Trial (Conclusion):
Forensic Botany: https://botany.org/home/resources/plant-talking-points/crime-scene-botanicals-forensic-botany.html