fibers

Fibers

Fibers

2Kendall/Hunt Publishing Company 2

You will understand:Why fibers are class evidence.

How fibers can be used as circumstantial evidence to link the victim, suspect, and crime scene.

Why statistics are important in determining the value of evidence.

Objectives

Fibers


You will be able to:Distinguish and identify different types of

fibers.

Understand polymerization.

Carry out an experiment in thin-layer chromatography.

Judge the probative value of fiber evidence.

Design and carry out scientific investigations.

Use technology and mathematics to improve investigations and communications.

Objectives, continued

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Are considered class evidence

Have probative value

-common fibers, such as white cotton and blue denim, have less probative value

Are common trace evidence at a crime scene

Can be characterized based on comparison of both physical and chemical properties

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Trace Evidence Can originate from

linen, furniture, clothing, carpet, insulation, or rope

The more fibers collected from different parts of suspects, the easier it is to link the suspect to the crime scene if all those fibers are found

Locard Principle Fibers can be left

behind and picked up by suspect and/or victim

Fibers are used to create a LINK between suspect and crime

Kendall/Hunt Publishing Company 5

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Direct Transfer Fibers directly from

victim to suspect Fibers directly from

suspect to victim

Secondary Transfer Victim has fibers on

him that he/she picked up from elsewhere and transferred them to suspect

Suspect picked up fibers from elsewhere and transferred the to victim


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Early Collection CRITICAL With in 24 hours, 95% may

have fallen from victim or been lost at a crime scene

Collect from scene and victims body (and any suspects if available)

Only fibers not expected to be found at the scene are investigated

Example: Would you

examine pink fibers on a victim if she lived in a house with wall to wall pink carpeting?


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Questions a Forensic Scientist Must Ask When Analyzing Fibers Type of Fiber

Composition; common or rare; what suspect/victim/part of crime scene had fiber on them/it? Fiber Color

Does color of suspects clothes match the color of the fiber found on victim/scene? Is it the same dye? Number of Fibers Found

How many fibers—1 or 100?More fibers =possibly more violence/struggle or longer contact Where the fiber was found

How close can you place suspect to the scene of the crime? Textile the fiber originated from

From carpet, upholstery, car, etc. Multiple Fiber transfers

Is there only one type or many different types at the scene? More sources suggest longer contact or possible violence. Type of crime committed

Was it violent, breaking and entering , kidnapping? Each type of crime has expected pattern of contact between suspect, victim and scene that is reflected in transfer of fibers.

Time between crime and discovery of the fiber How long ago did transfer take place—an hour ago, a day, a week? Unless the fiber location is undisturbed, the value of the

fiber found is gradually reduced as time goes by (b/c fibers will be expected to fall off or fibers not related to crime can be picked up)

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Terms

Textile Things like carpeting,

clothing, upholstery Constructed by

weaving or intertwining yarns

Yarns Made up of fibers

that are spun together


Fibers


Fabric

Fabric is made of fibers. Fibers are made of twisted filaments.

Types of fibers and fabric:Natural—animal, vegetable, or inorganicArtificial—synthesized or

created from altered natural sources

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Types of Fibers

Synthetic

Rayon

Nylon

Acetate

Acrylic

Spandex

Polyester

Natural

Silk

Cotton

Wool

Mohair

Cashmere

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Classification

Natural fibers are classified according to their origin:

1.)Plants/Vegetable or cellulose

- seeds, fruits, stems and leaves

-cellulose (insoluble in water)

-short (2-5 cm)

2.) Animal or protein

3.) Mineral

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Cellulose Fibers

Cotton—vegetable fiber; strong, tough, flexible, moisture-absorbent, not shape-retentive

Rayon—chemically altered cellulose; soft, lustrous, versatile

Cellulose acetate—cellulose that is chemically altered to create an entirely new compound not found in nature

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Fiber Comparison

Can you describe the difference(s) between the cotton onthe left and the rayon on the right?

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Animal Fibers

3 sources Hair

Brushed out of animals coat Shed or clipped Wool is most common animal hair used in textiles

Fur Skin of animal treated, remains flexible and retains fur…found in coats and

gloves Not a textile

Webbing Ex. Silk Collected from a cocoon of caterpillar Bombax mori Fibers very long , they tend to not shed as easily as hair fibers


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Protein Fibers

Wool—animal fiber coming most often from sheep, but may be goat (mohair), rabbit (angora), camel, alpaca, llama, or vicuña

Silk—insect fiber that is spun by a silkworm to make its cocoon; the fiber reflects light and has insulating properties

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Mineral Fibers ( come from rocks)

Asbestos—a natural fiber that has been used in fire-resistant substances

Rock wool—a manufactured mineral fiber

Fiberglass—a manufactured inorganic fiber

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Synthetic FibersMade from derivatives of petroleum, coal, and natural gas

Nylon—most durable of man-made fibers; extremely lightweight

Polyester—most widely used man-made fiber

Acrylic—provides warmth from a lightweight, soft, and resilient fiber

Spandex—extreme elastic properties

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Fabric Production

Fabrics are composed of individual threads or yarns that are made of fibers and are knitted, woven, bonded, crocheted, felted, knotted, or laminated. Most are either woven or knitted. The degree of stretch, absorbency, water repellence, softness, and durability are all individual qualities of the different fabrics.

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Weave Terminology

Yarn—a continuous strand of fibers or filaments that may be twisted together

Warp—lengthwise yarn

Weft—crosswise yarn

Blend—a fabric made up of two or more different types of fibers

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Weave Patterns

•Basket•Leno

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Plain Weave

The simplest and most common weave pattern

The warp and weft yarns pass under each other alternately

Design resembles a checkerboard

Characteristics:

Firm and wears well

Snag resistant

Low tear strength

Tends to wrinkle

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Twill WeaveThe warp yarn is passed over one to three

weft yarns before going under one.

Makes a diagonal weave pattern.

Design resembles stair steps.

Denim is one of the most common examples.

Characteristics:

Very strong

dense and compact

different faces;

diagonal design on surface

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Satin Weave

The yarn interlacing is not uniform

Creates long floats

Interlacing weave passes over four or more yarns

Satin is the most obvious example

Characteristics:

Not durable

Tends to snag and break during wear

Shiny surface

Little friction with other garments

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Basket

Alternating pattern of two weft threads crossing two warp threads

Characteristics: Does not wrinkle Open, porous weave Not very durable Shrinks when washed Tends to distort as yarn shifts


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Leno This uses two warp threads and a double weft thread The two adjacent warp threads cross over one

another. The weft travels left to right and is woven between

the two warp threads Characteristics:

Open weave Easily distorted with wear and washing Stretches in one direction


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Knitted Fabric

Knitted fabrics are made by interlocking loops into a specific arrangement.

It may be one continuous thread or a combination.

Either way, the yarn is formed into successive rows of loops and then drawn through another series of loops to make the fabric.

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Polymers

Synthetic fibers are made of polymers, which are long chains of repeating chemical units.

The word polymer means many (poly) units (mer).

The repeating units of a polymer are called monomers.

By varying the chemical structure of the monomers or by varying the way they are joined together, polymers are created that have different properties.

As a result of these differences, they can be distinguished from one another forensically.

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Filament Cross Sections

Synthetic fibers are forced out of a nozzle when they are hot, and then they are woven. The holes of the nozzle are not necessarily round; therefore, the fiber filament may have a unique shape in cross section.

R ound 4-lobed

Octalobal

Irregular

Multi-lobedor Serrate

T rilobal

Dogbone orDumbbell

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Testing for Identification

Microscopic observation

Burning—observation of how a fiber burns, the odor, color of flame, color of smoke, and the appearance of the residue

Thermal decomposition—gently heating to break down the fiber to the basic monomers

Chemical tests—solubility and decomposition

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Testing for Identification

Density—the mass of an object divided by the volume of the object

Refractive index—measurement of the bending of light as it passes from air into a solid or liquid

Fluorescence—absorption and reemission of light; used for comparing fibers as well as spotting fibers for collection

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Using Density 1 cc = 1 cm3 =1 mL D= mass/ vloume…. Measured using “g/cc” Used to confirm a fiber Useful for single fibers and are non-destructive Use columns with specific liquids to analyze

density


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Using Refractive Index


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Dyes

Components that make up dyes can be separated and matched to an unknown.

There are more than 7,000 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.

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Collection of Fiber Evidence

Bag clothing items individually in paper bags. Make sure that different items are not placed on the same surface before being bagged.

Make tape lifts of exposed skin areas and any inanimate objects.

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

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Fiber Evidence

Fiber evidence in court cases can be used to connect the suspect to the victim or to the crime scene. In the case of Wayne Williams, fibers weighed heavily on the outcome of the case. Williams was convicted in 1982 based on carpet fibers that were found in his home, in his car, and on several murder victims.

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More about Fibers

For additional information about fibers and other trace evidence, check out truTV’s Crime Library at:

www.crimelibrary.com/criminal_mind/forensics/trace/1.html

fibers

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