Trace Evidence l: Hairs and Fibers - Weeblyhenrysci.weebly.com/.../2/7/0/22702252/hairs_and_fibers.pdf · 2019-09-11 · Hairs and Fibers Chapter 10 . 10-2 PRENTICE HALL ©2008 Pearson

Trace Evidence l: Hairs and Fibers

Chapter 10

10-2

PRENTICE HALL

©2008 Pearson Education, Inc.

Upper Saddle River, NJ 07458

FORENSIC SCIENCE

An Introduction

By Richard Saferstein

Introduction • Hair

– encountered as physical evidence

– wide variety of crimes

– not yet possible to individualize a human hair to any single head or body through its morphology

• Strong corroborative evidence

– placing an individual at a crime scene

– properly collected and submitted to the lab

– accompanied with adequate number of reference samples

10-3

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An Introduction


Morphology of Hair • Hair

– appendage of the skin that grows out of the hair follicle

– length of hair extends from its root (bulb embedded in the follicle), into a shaft, and terminates at a tip (end)

• Shaft

– three layers—the cuticle, cortex, and medulla

– subjected to the most intense examination

10-4

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FORENSIC SCIENCE

An Introduction


Anatomy of Single Strand of Hair

10-5

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An Introduction


Cuticle and Cortex • Cuticle

– scale structure covering the exterior of the hair

• always point towards the tip of the hair

• pattern is useful in species identification

• Cortex

– main body of the hair shaft

– embedded with pigment granules that give hair color

– The color, shape, and distribution of these granules provide points of comparison among the hairs of different individuals

10-6

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An Introduction


Cuticle Scale Patterns

Rabbit/

Mouse

Cat/ Fox

Humans

10-7

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FORENSIC SCIENCE

An Introduction


Medulla • Cellular column running through the center of the

hair

– Medullary index = diameter of medulla / diameter of hair shaft

– For humans, the medulla generally occupies < 1/3 the diameter of the shaft, while for animals it is >1/2.

– continuous, interrupted, fragmented or absent

– The presence varies from individuals and even among hairs of a given individual.

– different shapes, depending the species

10-8

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An Introduction


Medulla Patterns in Humans

10-9

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FORENSIC SCIENCE

An Introduction


Animal Medulla Patterns

Dog Cow Deer Fox Mouse

Rabbit Raccoon

10-10

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FORENSIC SCIENCE

An Introduction


Root • Provides the tools necessary to

produce hair and continue its growth

• Follicular tag – translucent tissue surrounding the hair’s

shaft near the root when forcibly removed

–Using DNA analysis, the hair may be individualized

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An Introduction


Comparing Strands

• Use the comparison microscope

• Matching the color, length, and diameter

• Microscopic examination will reveal morphological features that distinguish human and animal hair

• Important for identification – Scale structure

– Medullary index

– Medullary shape

10-12

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An Introduction


Comparing Strands

• Other important features for comparing human hair are: – the presence or absence of a medulla.

– the distribution, shape, and color intensity of the pigment granules present in the cortex.

• Most common request determine if hair recovered at crime scene matches hair removed from suspect

• Microscopic hair examinations tend to be subjective and highly dependent on the skills and integrity of the analyst.

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An Introduction


Questions

• Can the body area from which a hair originated be determined?

• Can the racial origin of hair be determined?

• Can the age and sex of an individual be determined from a hair sample?

• Is it possible to determine if a hair was forcibly removed from the body?

• Are efforts being made to individualize human hair?

• Can DNA individualize a human hair?

10-14

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An Introduction


Mongoloid (Asian Descent)

Hairs will

– be very coarse

– contain larger pigment granules than Caucasoid hair

– contain a thick medulla

– be straight

– have completely round

cross section

10-15

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An Introduction


Caucasoid (European Descent)

• Hairs will

– be fine to slightly coarse

– range in color from very light to dark

– be generally straight or with slight waves

– have slightly oval shaped cross section

10-16

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An Introduction


Negroid (African Descent) • Hairs will

– be medium coarse

– contain the largest pigment granules

– Have flatter cross section

– often have split ends

– be kinky or curly

10-17

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An Introduction


10-18

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An Introduction


Hair and DNA

• DNA profiling has extended to the individualization of human hair

• Hair in the anagen phase has a higher probability of containing DNA in hair roots than hair in the catagen or telogen phases

• The follicular tag may still be present if hair was forcibly removed

– This has proven to be a rich source of nuclear DNA

associated with hair.

10-19

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An Introduction


Phases of Hair Growth

Anagen

• Actively growing

• 85% of hair

• Forcibly removed

• Generally retains follicular tag

Telogen

• Hair stopped growing

• 12-15% of hair

• Hair may readily fall out

• Does not retain follicular tag

10-20

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An Introduction


Hair and Mitochondrial DNA

• Mitochondrial DNA can be extracted from the hair shaft.

– Mitochondrial DNA is found in cellular material located outside of the nucleus and it is transmitted only from the mother to child.

• All positive microscopical hair comparisons must be confirmed by DNA analysis.

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An Introduction


Collection and Preservation

• Forensic hair comparisons involve either head hair or pubic hair.

• 50 full-length hairs from all areas of the scalp will ensure a representative sampling of head hair

• 24+ full-length pubic hairs should cover the range of characteristics present in pubic hair.

• Hair samples are also collected from the victim of suspicious deaths during an autopsy.

10-22

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An Introduction


Types of Fibers

• Natural fibers are derived in whole from animal or plant sources. – Plants – seeds, fruits, stems, leaf

• Seeds – cotton

• Fruits – coir

• Stems – hemp, jute, flax (linen)

• Leaf – manila sisal

– Animals – wool, mohair, cashmere, angora, furs, silk

– Minerals – asbestos, fiberglass

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An Introduction


Types of Fibers • Man-made fibers are manufactured.

– Regenerated fibers are manufactured from natural raw materials

– Ex: rayon, acetate, triacetate

– Synthetic fibers are produced solely from synthetic chemicals

– Ex: nylons, polyesters, acrylics, olefins

• Polymers are synthetic fibers composed of a large number of atoms arranged in repeating units known as monomers.

10-24

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An Introduction


Fiber Evidence • Class evidence

• The quality of fiber evidence depends on

– ability to identify the origin of the fiber

– at least narrow the possibilities to a limited number of sources

• Individual evidence

– If the examiner is presented with fabrics that can be exactly fitted together at torn edges

10-25

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An Introduction


Fiber Evidence • Microscopic comparisons between questioned

and standard/reference fibers

– initially for color and diameter characteristics

– weave pattern

• Other features in comparing fibers are:

– Lengthwise striations on the surface of the fiber

– Delustering particles that reduce shine

– The cross-sectional shape of the fiber

• Compositional differences may exist in the dyes applied during manufacturing process

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An Introduction


Methods for Fiber Comparison

• The visible light microspectrophotometer – convenient way to compare the colors of fibers through

spectral patterns. • Chromatographic separation

– more detailed analysis of the fiber’s dye composition • Infrared spectrophotometry

– rapid and reliable method for identifying the generic class of fibers

• Polarizing microscope. – rapid and reliable method for identifying the generic class

of fibers – Depending on the class of fiber, each will have a

characteristic index of refraction

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An Introduction


Collection and Preservation • The investigator’s task of looking for minute

strands of fibers often becomes one of identifying and preserving potential “carriers” of fiber evidence.

• Relevant articles of clothing should be packaged carefully in separate paper bags.

• If it is necessary to remove a fiber from an object, the investigator must use clean forceps, place it in a small sheet of paper, fold and label the paper, and place the paper packet inside another container.

10-28

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An Introduction


Silk

• Comes from the silk worm’s cocoon • http://www.micktravels.com/china/silk.html

http://www.micktravels.com/china/silk.html

http://www.micktravels.com/china/silk.html

Documents

Trace Evidence l: Hairs and Fibers - Weeblyhenrysci.weebly.com/.../2/7/0/22702252/hairs_and_fibers.pdf · 2019-09-11 · Hairs and Fibers Chapter 10 . 10-2 PRENTICE HALL ©2008 Pearson