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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 .