Trace EvidenceTrace Evidence

What do you think What do you think trace evidence is?trace evidence is?

Materials that are small enough Materials that are small enough to be easily overlooked by a to be easily overlooked by a crime scene investigatorcrime scene investigator

They are so small they can be They are so small they can be transferred (exchanged) by transferred (exchanged) by contact or in the air by air contact or in the air by air currents!currents!

Locard’s exchange Locard’s exchange Principle?Principle?

• WhenWhen 2 objects come in 2 objects come in contact with each other, a contact with each other, a cross-transfer of materials cross-transfer of materials occursoccurs

Types of Trace Types of Trace evidenceevidence

• HairHair• Fibers & threadsFibers & threads• MetalsMetals• Paint & other building Paint & other building

materialsmaterials• Soil, rocks, minerals, & debrisSoil, rocks, minerals, & debris• String, rope, & containersString, rope, & containers• Wood & plant materialWood & plant material

Anatomy of HairAnatomy of Hair

• Root (internal end)Root (internal end)• MedullaMedulla– Inner coreInner core– May or may not be presentMay or may not be present

• Cortex – main shaft Cortex – main shaft surrounding the medullasurrounding the medulla

• Cuticle – scaly outer coveringCuticle – scaly outer covering• Tip (external end)Tip (external end)

Medulla PatternsMedulla Patterns

1.1. Continuous – a solid lineContinuous – a solid line2.2. Interrupted – broken at Interrupted – broken at

regular intervals, like the regular intervals, like the dotted yellow lines on a roaddotted yellow lines on a road

3.3. Fragmented – broken, but not Fragmented – broken, but not in a regular patternin a regular pattern

4.4. AbsentAbsent

Anatomy of HairAnatomy of Hair

Human, cat, Dog, Human, cat, Dog, and Mouse Hairand Mouse Hair

What can hair tell What can hair tell us?us?

• We know it can tell us We know it can tell us whether the hair is human or whether the hair is human or not.not.

• If human:If human:– RaceRace– Pulled out or fell out?Pulled out or fell out?– Part of the body it came fromPart of the body it came from– How it was cut or dressedHow it was cut or dressed

• If animal, what species?If animal, what species?

Phases of Hair Phases of Hair GrowthGrowth

Location of OriginLocation of Origin• Scalp hairScalp hair– Little diameter variationLittle diameter variation– More uniform distribution of More uniform distribution of

pigmentpigment– No medulla or fragmentedNo medulla or fragmented

• Pubic hairPubic hair– Short and curlyShort and curly– Wide variations in diameterWide variations in diameter– Continuous medullaContinuous medulla

• Beard hairBeard hair

Collecting the Collecting the EvidenceEvidence

• About 40-50 samples from the About 40-50 samples from the scalpscalp

• About 24 full-length pubic About 24 full-length pubic hairshairs

• Need entire hair:Need entire hair:– Variations in color and other Variations in color and other

features alng length of hairfeatures alng length of hair• Collected how???Collected how???

Hair Analysis at Hair Analysis at WorkWork

• Ennis CosbyEnnis Cosby• Central Park JoggerCentral Park Jogger– Microscopic analysis vs. DNA Microscopic analysis vs. DNA

analysisanalysis

Hair Needed!Hair Needed!

• Bring in samples of pet hair!Bring in samples of pet hair!• Try to find hairs that have Try to find hairs that have

fallen out. (Where should you fallen out. (Where should you look?)look?)

• Beard hair anyone?Beard hair anyone?