Trace Evidence

What do you think trace evidence is? Materials that are small enough to be easily overlooked by a crime scene investigator They are so small they can be transferred (exchanged) by contact or in the air by air currents!

Locard’s exchange Principle ? When 2 objects come in contact with each other, a cross-transfer of materials occurs

Types of Trace evidence Hair Fibers & threads Metals Paint & other building materials Soil, rocks, minerals, & debris String, rope, & containers Wood & plant material

Anatomy of Hair Root (internal end) Medulla Inner core May or may not be present Cortex – main shaft surrounding the medulla Cuticle – scaly outer covering Tip (external end)

Medulla Patterns Continuous – a solid line Interrupted – broken at regular intervals, like the dotted yellow lines on a road Fragmented – broken, but not in a regular pattern Absent

Anatomy of Hair

Human, cat, Dog, and Mouse Hair

What can hair tell us? We know it can tell us whether the hair is human or not. If human: Race Pulled out or fell out? Part of the body it came from How it was cut or dressed If animal, what species?

Phases of Hair Growth

Location of Origin Scalp hair Pubic hair Beard hair Little diameter variation More uniform distribution of pigment No medulla or fragmented Pubic hair Short and curly Wide variations in diameter Continuous medulla Beard hair

Collecting the Evidence About 40-50 samples from the scalp About 24 full-length pubic hairs Need entire hair: Variations in color and other features alng length of hair Collected how???