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Intro to Hair and Fiber EvidenceForensic Science 4/13/15

+Drill

How was hair/fiber evidence used in the Jeffrey MacDonald case?

List four different types of hair or fiber evidence that you could leave behind or pick up over the course of a day.

HW: Work on Ch 8 10 Fill in the Blank Questions

+Objectives

IWBAT Describe the cuticle, cortex, and medulla of

a hair. List hair features that are useful for

examining human hairs.

+IntroductionHair is encountered as physical evidence in a wide variety of crimes.

Although it is not yet possible to individualize a human hair to any single head or body through its morphology, it still has value as physical evidence.

When properly collected and submitted to the laboratory accompanied by an adequate number of standard/reference samples, hair can provide strong corroborative evidence for placing an individual at a crime scene.

+Morphology of HairHair is an appendage of the skin that grows out of an organ known as the hair follicle.

The length of a hair extends from its root or bulb embedded in the follicle, continues into a shaft, and terminates at a tip end.

It is the shaft, which is composed of three layers—the cuticle, cortex, and medulla—that is subjected to the most intense

examination by the forensic scientist.

+Hair grows from a follicle

+Hair cross section

Outer layer; overlapping scales like shingles on a roofMiddle layer; elongated cells; may contain pigment granules

Innermost layer; composed largely of air spaces and soft keratin

+Cuticle and Cortex

The cuticle is the scale structure covering the exterior of the hair. The scales always point towards the tip of the

hair. The scale pattern is useful in species

identification.

The cortex is the main body of the hair shaft. Its major forensic importance is the fact that it is

embedded with the pigment granules that impart hair with color.

The color, shape, and distribution of these granules provide the criminalist with important points of comparison among the hairs of different individuals.

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Characteristics of the cuticle may be important in distinguishing between hairs of different species but are often not useful in distinguishing between different people.

Info: http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair Image: http://www.hairdressersus.com/micro/Image5b.jpg

Hair Structure

Cuticle

The cuticle varies in:• Its scales,

How many there are per centimeter, How much they overlap, Their overall shape, and How much they protrude from the surface

• Its thickness, and • Whether or not it contains pigment.

+Cuticle

Varies by speciesCoronal (rodents, bats)Imbricate (large mammals, humans)

http://www.microlabgallery.com/gallery/hair%20scale.aspx

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Cortex

The cortex varies in:• Thickness• Texture• Color

• Distribution of the cortex is perhaps the most important component in determining from which individual a human hair may have come.

• Microscopic examination can also reveal the condition and shape of the root and tip.

Info: http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair Image: http://www.extrapersonality.com/hair.html

Hair Structure

+Cortex

Ovoid body

Pigment granules

Dog hairHuman hair

Cortical fusi

Pigment granules

+MedullaThe medulla is a cellular column running

through the center of the hair. The medullary index measures the diameter

of the medulla relative to the diameter of the hair shaft.

For humans, the medulla generally occupies less than one-third the diameter of the shaft, while for animals it is generally one-half or greater.

The medulla may be continuous, interrupted, fragmented or absent.

The presence of the medulla varies from individual to individual and even among hairs of a given individual.

Medullae also have different shapes, depending the species.

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MedullaThe medulla may vary in:

• Thickness• Continuity - one continuous structure

or broken into pieces• Opacity - how much light is able to

pass through it

• It may also be absent in some species.

http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair

Like the cuticle, the medulla can be important for distinguishing between hairs of different species, but often does not lend much important information to the differentiation between hairs from different people.

Hair Structure

http://www.bfro.net/images/whatis/figures/Fig.%203%20with%20caption.jpg

+Medulla

http://www.microlabgallery.com/gallery/hair%20medulla.aspx

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Beaver (continuous)

Mink (ladder)

Moose (lattice)

+The medulla can vary within and between individuals

+RootThe root and other surrounding cells in the hair follicle provide the tools necessary to produce hair and continue its growth.

When pulled from the head, some translucent tissue surrounding the hair’s shaft near the root may be found. This is called a follicular tag.

By using DNA analysis on the follicular tag, the hair may be individualized.

+How was it lost?

http://www.fbi.gov/about-us/lab/forensic-science-communications/fsc/jan2004/research/2004_01_research01b.htm

Natural shedding, e.g. found in a hairbrush

Forcibly removed during its growth stage

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http://www.fbi.gov/about-us/lab/forensic-science-communications/fsc/jan2004/research/2004_01_research01b.htm

Burned Freshly razor cut Abraded

Broken Freshly cut with scissors

+Comparing Strands

The comparison microscope is an indispensable tool for comparing the morphological characteristics of hair.

When comparing strands of human hair, the criminalist is particularly interested in matching the color, length, and diameter.

A careful microscopic examination of hair will reveal morphological features that can distinguish human hair from the hair of animals.

Scale structure, medullary index, and medullary shape are particularly important in animal hair identification.

+Is it human?

Human

Pigment evenly distributed or concentrated near cuticle

Color consistent along length of shaft

Medulla is amorphous or absent

Medulla occupies <1/3 diameter of hair

Cuticle is imbricate

Root is club-shaped

Nonhuman

Pigment generally concentrated near medulla

Often bands of color alternating down shaft

Medulla generally continuous and/or structured

Medulla occupies >1/3 the diameter of hair

Cuticle varies with species

Root shape varies

+Comparing StrandsOther 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.

The most common request is to determine whether or not hair recovered at the crime scene compares to hair removed from the suspect.

However, microscopic hair examinations tend to be subjective and highly dependant on the skills and integrity of the analyst.

+Hair and DNA

Recent major breakthroughs in DNA profiling have extended this technology to the individualization of human hair.

The probability of detecting DNA in hair roots is more likely for hair being examined in its anagen or early growth phase as opposed to its catagen (middle) or telogen (final) phases.

Often, when hair is forcibly removed a follicular tag, a translucent piece of tissue surrounding the hair’s shaft near the root, may be present.

This has proven to be a rich source of nuclear DNA associated with hair.

+Hair and Mitochondrial DNA

Mitochondrial DNA can be extracted from the hair shaft.

As a rule, all positive microscopical hair comparisons must be confirmed by DNA analysis.

+Collection and Preservation

As a general rule, forensic hair comparisons involve either head hair or pubic hair.

The collection of 50 full-length hairs from all areas of the scalp will normally ensure a representative sampling of head hair.

A minimum collection of two dozen 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.

+ Racial Differences in Hair Put this on the back page, in a table.Race Appearanc

ePigment Granules

Cross Section

Other

European

Generally straight or wavy

Small and evenly distributed

Oval or round of moderate diameter, minimal variation

May be blond, red, brown, or black

+Race Appearance Pigment Granules

Cross Section

Other

Asian Straight Densely distributed

Round with large diameter

Shaft tends to be coarse and straightThick cuticleContinuous medulla

+Race Appearance Pigment Granules

Cross Section

Other

African Kinky, curly, or coiled

Densely distributed, clumped, may differ in shape and size

Flattened with moderate to small diameter and considerable variation

+Types of Fibers Natural fibers are derived in whole from

animal or plant sources. Examples: wool, mohair, cashmere, furs, and

cotton.

Man-made fibers are manufactured. Regenerated fibers are manufactured from

natural raw materials and include rayon, acetate, and triacetate.

Synthetic fibers are produced solely from synthetic chemicals and include nylons, polyesters, and acrylics.

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

Many different natural fibers that come from plants and animals are used in the production of fabric.

http://www.fireflydiapers.com/articles/diaperarticle_naturalfibersabsorb.htm

Cotton fibers are the plant fibers most commonly used in textile materials

The animal fiber most frequently used in the production of textile materials is wool, and the most common wool fibers originate from sheep.

Natural Fibers

Images: http://www.trashforteaching.org/phpstore/product_images/YarnWS.JPG http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric3.htm#Fiber%20Evidence

http://www.jivepuppi.com/images/fiber_evidence.jpg

More than half of all fibers used in the production of textile materials are synthetic or man-made.

Nylon, rayon, and polyester are all examples of synthetic fibers.

Cross-section of a man-made fiber

Synthetic Fibers

Fibers under a microscope

+Fiber EvidenceThe quality of the fiber evidence

depends on the ability of the criminalist to identify the origin of the fiber or at least be able to narrow the possibilities to a limited number of sources.

Obviously, if the examiner is presented with fabrics that can be exactly fitted together at their torn edges, it is a virtual certainty that the fabrics were of common origin.

+Fiber Evidence Microscopic comparisons between questioned

and standard/reference fibers are initially undertaken for color and diameter characteristics, using a comparison microscope.

Other morphological features that could be important in comparing fibers are: Lengthwise striations on the surface of the fiber. The presence of delustering particles that reduce

shine. The cross-sectional shape of the fiber.

Compositional differences may exist in the dyes that were applied to the fibers during the manufacturing process.

+ Methods for Fiber ComparisonThe visible light microspectrophotometer

is a convenient way for analysts to compare the colors of fibers through spectral patterns.

A more detailed analysis of the fiber’s dye composition can be obtained through a chromatographic separation.

Infrared spectrophotometry is a rapid and reliable method for identifying the generic class of fibers, as does the polarizing microscope.

Depending on the class of fiber, each polarized plane of light will have a characteristic index of refraction.

+ 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.

+Closure

Write: 3 ways to tell if a hair is human How can you figure out who the hair came

from?