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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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
Anatomy of Single Strand of Hair
10-5
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
Cuticle Scale Patterns
Rabbit/
Mouse
Cat/ Fox
Humans
10-7
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
Medulla Patterns in Humans
10-9
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
Animal Medulla Patterns
Dog Cow Deer Fox Mouse
Rabbit Raccoon
10-10
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
10-11
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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.
10-13
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
10-18
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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.
10-21
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
10-23
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
10-26
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
10-27
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
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
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
Silk
• Comes from the silk worm’s cocoon • http://www.micktravels.com/china/silk.html