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):

https://www.ojp.gov/ncjrs/virtual-library/abstracts/fiber-evidence-and-wayne-williams-trial-conclusion

Forensic Botany: https://botany.org/home/resources/plant-talking-points/crime-scene-botanicals-forensic-botany.html