CRIMINAL MISCHIEF 53: Forensic Science For Crime Writers: Trace Evidence

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

 

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