Unit 4: Trace Evidence (Hair & Fiber)

Hair Analysis

It’s usually class evidence

-unless DNA in root is found (can sometimes do mtDNA testing)

Hair even varies within a single person

Hair is found only in mammals

What can be determined from hair: If the source is human or animal Race (sometimes) Origin of the location on the source’s body Whether the hair was forcibly removed If the hair has been treated with chemicals If drugs have been ingested or if person has

been exposed to toxins Individualized if root is present (DNA)

Things hair can’t determine:

• Age (except infant hair)

• Gender (unless DNA in root)

Tools of the Trade

View of hairs using a

comparison-light microscope

comparison-light microscope

$1850 +

Microspectrophotometry

The exact color of an object is measured via light absorption & reflection

$30,000 +

Scanning Electron Microscope Uses electron

beam

Up to 100,000 x

pollen

$ 250 K – 1 million

Structure of Hair Outgrowth of the skin

Hair is made of dead cells that have a hard protein coating, called keratin on the outer layer.

Hair grows out of the follicle (new cells push the old ones up and out).

Hair Growth Grows approximately 0.5 inch per month

You lose about 35-40 hairs/ day

Hair Life Cycle

Forcible Removal of Hair

Naturally shed hairs = undamaged, club-shaped roots.

Forcibly removed

hairs = may have

tissues attached

Forcibly removed

hairs = may have

stretched root

From http://www.fbi.gov/about-us/lab/forensic-sciencecommunications/fsc/july2000/deedric1.htm.

Hair Structure

Hair is composed 3 main parts :

Cuticle—outside covering, made of overlapping scales

Cortex—inner layer made of keratin and imbedded with pigment

Medulla—inside layer running down the center of the cortex

The Cuticle outermost layer of hair which is

covered with scales.

The scales point toward the tip of the hair.

IMPORTANCE: Scales differ between species of animals

The three basic patterns are:

Cuticle (scales) ComparisonsScales on bat hair Scales on human hair

Scales on moose hair

The Cortex

gives the hair its

color

IMPORTANCE: Melanin—pigment granules that give hair its color and a good point of comparison.

The Medulla The medulla is the hair

core that is not always visible.

IMPORTANCE: The medulla comes in different types, patterns, and thickness.

Images from Brennon Sapp and bsapp.com.

Medulla Comparisons

Humans have a small medulla (less than 1/3 of the hair diameter)

Animals have larger medulla (1/2 hair diameter + )

Medullas in animals sometimes exhibit patterned shapes (humans are usually cylindrical)

Images from Brennon Sapp and bsapp.com.

Ex of Animal Hair-medulla size and shape

Hair Comparison- Error rates (study done by FBI)

Hair evidence (1996-2000) was DNA tested & microscopic examination

11% of hairs that were ―matches‖ by examiners via microscopes were actually non-matches according to DNA.

Conclusion: Microscopic matches are presumptive in nature and must be confirmed by DNA.

Is it a match?

Central Park Jogger Case

5 teens convicted of brutally beating & raping “Central Park Jogger” (1989)

Evidence: confessions by teens & hair on one defendant that “resembled” victim.

Another man came forward & confessed to crime & had matching DNA (2002)

Individualizing Hair (DNA) Nuclear DNA (in the root).

Mitochondrial DNA (mtDNA) Hair shaft contains abundant inherited only from the mother. Process is more difficult and costly than using nuclear DNA. Can only narrow it down to siblings, not an individual

Collection of Hair Questioned hairs must be

accompanied by an adequate number of control samples. from victim

from possible suspects

from others who may have deposited hair at the scene

Control Sample 50 full-length hairs from all

areas of scalp

24 full-length pubic hairs

Hair Toxicology

Advantages: Easy to collect and store

Is externally available

Can provide information on the individual’s history of drug use or of poisoning.

Collections must be taken from different locations on the body to get an accurate timeline.

Hair Toxicology

By analyzing his hair, some investigators suggest he was poisoned by the deliberate administration of arsenic;

others suggest that it was vapors from the dyes in the wallpaper that did him in.

Napoleon died in exile in 1821.

FIBER ANALYSIS

Fiber Analysis

Are considered class evidence

(they are very hard to

individualize)

Have probative value (can

prove something)

common at a crime scene

Analyzed based on physical &

chemical properties

2 Main Types of Fibers:

Synthetic

-had to learn how to chemically manufacture polymers first) Rayon (1911)

Nylon (1939)

Acetate

Acrylic

Spandex

Polyester

Natural Silk

Cotton

Wool

Cashmere (goats)

ID and Comparison of Fibers

Can you tell the difference(s) between the cotton (left) & the rayon (right)?

1. Microscopic Examination

Weave Patterns(don’t need to know)

Filament Cross-Sections (don’t need to know)

Synthetic fibers are forced out of a nozzle when they are hot, and then they are woven.

Testing the Dyes(don’t need to know)

Components that make up dyes can be

separated and matched to an unknown.

There are more than 7000 different dye

formulations.

Chromatography is used to separate dyes for

comparative analysis.

The way a fabric accepts a particular dye

may also be used to identify and compare

samples.

Collection of Fiber Evidence

Bag clothing items individually in paper bags.

Make tape lifts of exposed skin areas of bodies/ objects

Removed fibers should be folded into a small sheet of paper and stored in a paper bag.

Vacuum collection system

Individual vs. Class EvidenceIndividual Evidence

Really high probability of being linked to one, unique source

Ex:– Fingerprints

1 x 1060 = probability of 2 people having same fingerprint

– DNA– Bullets– Tire/ footwear patterns– Tool marks– Broken glass

Class Evidence Object has

characteristic common to a group of similar objects

Ex:– Hair– Fibers– Blue jeans

Can increase the probability of class evidence by finding things that can make it unique:– Ex: stains, wear patterns

on jeans

Probability & Class Evidence Product Rule- Used to

determine the probability of finding a particular characteristic in a population.

Uses probability of each individually occurring and then multiply them together, you can determine the chances of all the characteristics occurring at one time.

increases the probative value of the class evidence.

Ex: suspect seen wearing a white t-shirt, jeans, and white tennis shoes.

Product Rule Example: Ex: Suspect seen leaving student parking lot where window was

broken & ipod stolen. Witness says suspect had: brown hair, wearing white shirt, and jeans. (assume: 1400 students) – Brown hair= 70% of students have– Maroon fibers = 10 % student have on– Black denim fiber= 2% students wearing

How many people should be called in?

(.7)(.1)(.2) = 0.014 or 1.4% of students will be wearing this combination of items.

Roughly 20 students/1400 .