Chapter 6: Fibers

“Wherever he steps, whatever he touches, whatever he leaves even unconsciously, will serve as silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool marks he leaves, the paint he scratches, the blood or semen he deposits or collects—all of these and more bear mute witness against him. This is evidence that does not forget.”

—Paul L. Kirk (1902 – 1970)-Forensic scientist

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Fibers

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

Why fibers are class evidence.

Why statistics are important in determining the value of evidence.

The student will learn:

Students will learn:

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Fibers

Are considered class evidence Have 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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Fibers at the Crime Fibers at the Crime SceneScene

Can occurCan occur When two people come in contactWhen two people come in contact When contact occurs with an item from the When contact occurs with an item from the

crime scenecrime scene Methods of transferMethods of transfer

Direct transferDirect transfer — fiber transferred from — fiber transferred from fabric directly onto victim or suspectfabric directly onto victim or suspect

Indirect transferIndirect transfer — fibers already transferred — fibers already transferred onto clothing of suspect or victim transfer onto onto clothing of suspect or victim transfer onto the other partythe other party

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Forensics of Fiber Forensics of Fiber AnalysisAnalysis

Cross transfers of fiber often occur in cases in Cross transfers of fiber often occur in cases in which there is person-to-person contact which there is person-to-person contact

Investigators hope that fiber traceable back to Investigators hope that fiber traceable back to the offender can be found at the crime scene, the offender can be found at the crime scene, as well as vice versa.as well as vice versa.

Success in solving crimes often hinge on the Success in solving crimes often hinge on the ability to narrow the sources for the type of ability to narrow the sources for the type of fiber found, as the prosecution did with their fiber found, as the prosecution did with their probability theory on the fibers probability theory on the fibers

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Fiber EvidenceFiber Evidence

Fibers are gathered at a crime scene with Fibers are gathered at a crime scene with tweezers, tape, or a vacuum. tweezers, tape, or a vacuum. 

They generally come from clothing, They generally come from clothing, drapery, wigs, carpeting, furniture, and drapery, wigs, carpeting, furniture, and blankets.  blankets. 

For analysis, they are first determined to For analysis, they are first determined to be natural, manufactured, or a mix of be natural, manufactured, or a mix of both.both.

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Collection ofFiber 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 of bodies 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, car and on several murder victims.

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Fiber EvidenceFiber Evidence The problem with fiber evidence is that fibers The problem with fiber evidence is that fibers

are not unique. are not unique.  Unlike fingerprints or DNA, they cannot Unlike fingerprints or DNA, they cannot

pinpoint an offender in any definitive manner.  pinpoint an offender in any definitive manner.  There must be other factors involved, such as There must be other factors involved, such as

evidence that the fibers can corroborate or evidence that the fibers can corroborate or something unique to the fibers that set them something unique to the fibers that set them apart. apart.

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Fabric

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

Types of fibers and fabric Natural —animal, vegetable or

inorganic Synthetic (Artificial) —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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Identification of FibersIdentification of Fibers

PlantPlant ( (vegetable) fibersvegetable) fibers are are characterized by anatomical features. characterized by anatomical features.

Animal fibersAnimal fibers are recognized by their are recognized by their morphology and classified into major morphology and classified into major groups. groups.

SyntheticSynthetic and and regenerated fibersregenerated fibers are are characterized by polarized light characterized by polarized light microscopy. microscopy.

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Fiber Comparison

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

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Classification

Natural fibers are classified according to their origin:

Plant fibers Animal fibers Mineral fibers

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Classification of fibers Classification of fibers by their compositionby their composition

Natural plant fibers may be more ribbon Natural plant fibers may be more ribbon shaped and may contain twists at shaped and may contain twists at irregular intervalsirregular intervals

Natural fibers from an animal source Natural fibers from an animal source look like hair and will often have rough look like hair and will often have rough external scale patterns and medullaexternal scale patterns and medulla

Synthetic fibers tend to be smooth and Synthetic fibers tend to be smooth and uniform and some may have long uniform and some may have long striations lines on the other layer striations lines on the other layer

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Plant Fibers Cotton —vegetable fiber; strong, tough, flexible,

moisture absorbent, not shape retentive Most common natural fiber Evidential value almost meaningless

Other plant fibers Flax (linen) Ramie Jute Hemp

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Other plant fibersOther plant fibers

Flax (linen)Flax (linen) RamieRamie JuteJute HempHemp

linen

ramie

jute

hemp

Flax fibers viewed wth polarized light

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Animal Fibers Most common animal fiber

Wool — sheep hair Fine wool found in clothing Coarse wool found in carpet common a

Other animal fibers Mohair and cashmere — goats Wool — camel hair Wool — llama hair Angora — rabbit hair Silk —insect fiber that is spun by a silk

worm (moth caterpillar) to make its cocoon Vicunas (looks like a llama - South

America) $3000 / bolt of their fir wool

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Mineral Fibers

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 fibersSynthetic fibers

More than half of all fibers used in production More than half of all fibers used in production of textile materials are man-madeof textile materials are man-made

Manufactured fibers can originate fromManufactured fibers can originate from Natural materialsNatural materials

Examples: rayon and acetateExamples: rayon and acetate

Synthetic materialsSynthetic materials Examples: nylon, polyester and acrylicExamples: nylon, polyester and acrylic

The amount of production of a particular man-The amount of production of a particular man-made fiber and its end use influence the degree made fiber and its end use influence the degree of rarity of a given fiberof rarity of a given fiber

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PolyesterPolyester

Red PolyesterRed Polyester Green PolyesterGreen Polyester

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Synthetic Fibers(Made from derivatives of petroleum,

coal and natural gas)

Nylon —most durable of man-made fibers; extremely light weight

Polyester —most widely used man-made fiber

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

Spandex —extreme elastic properties Rayon —chemically-altered cellulose; soft,

lustrous, versatile

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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, forensically they can be distinguished from one another.

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Synthetic (Man-Made) Synthetic (Man-Made) FibersFibers

The shape of a man-made fiber can The shape of a man-made fiber can determine the value placed on that determine the value placed on that fiber.fiber.

Cross section of a man-made fiber Cross section of a man-made fiber can be manufacturer-specific.can be manufacturer-specific.

Some cross sections are more Some cross sections are more common than others, and some common than others, and some shapes may only be produced for a shapes may only be produced for a short period of time.short period of time.

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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.

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Synthetic FibersSynthetic Fibers

Cross sections of nylon carpet Cross sections of nylon carpet fibers seen with a scanning fibers seen with a scanning electron microscope (SEM)electron microscope (SEM)

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Testing for Identification

Microscopic observation

Burning—observation of how a fiber burns, the odor, color of flame, 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—mass of object divided by the volume of the object

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

Fluorescence—used for comparing fibers as well as spotting fibers for collection

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Dyes 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.

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Identification and Comparison of Fibers

Fourier Transform Infrared analysis (FTIR) —based on selective absorption of wavelengths of light

Optical microscopy —uses polarizing light and comparison microscopes

Pyrolysis gas chromatography-mass spectrometry (PGC-MS) —burns a sample under controlled conditions, separates and analyzes each combustion product

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Fabric Production

Fabrics are composed of individual threads or yarns, made of fibers, that 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, either twisted or not

Warp—lengthwise yarn Weft—crosswise yarn Blend—a fabric made up of two or

more different types of fiber.

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Weave Patterns

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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

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Twill Weave

The 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

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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

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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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More about Fibers

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

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