Fibers

Fibers

Objectives
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.

Kendall/Hunt Publishing Company 22

Fibers

Objectives, continued
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.


Fibers

Fibers

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


Fibers

 Trace Evidence  Locard Principle
 Can originate from  Fibers can be left
linen, furniture, clothi behind and picked up
ng, carpet, insulation,
by suspect and/or
or rope
victim
 The more fibers
collected from different  Fibers are used to
parts of suspects, the create a LINK
easier it is to link the
suspect to the crime between suspect and
scene if all those fibers crime
are found


Fibers

 Direct Transfer  Secondary Transfer
 Fibers directly from  Victim has fibers on
victim to suspect him that he/she
 Fibers directly from picked up from
suspect to victim elsewhere and
transferred them to
suspect
 Suspect picked up
fibers from elsewhere
and transferred the to
victim

Fibers

 Early Collection CRITICAL  Example:
 With in 24 hours, 95% may  Would you
examine pink
have fallen from victim or been fibers on a
lost at a crime scene victim if she
 Collect from scene and lived in a
house with
victims body (and any wall to wall
suspects if available) pink
carpeting?
 Only fibers not expected to be
found at the scene are
investigated

Fibers
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)
88

Fibers
Terms

 Textile  Yarns
 Things like carpeting,  Made up of fibers
clothing, upholstery that are spun together
 Constructed by
weaving or
intertwining yarns


Fibers

Fabric

Fabric is made of fibers. Fibers
are made of twisted
filaments.
Types of fibers and fabric:
Natural—animal, vegetable, or
inorganic
Artificial—synthesized or
created from altered
natural sources


Fibers

Types of Fibers

Synthetic Natural
Rayon Silk
Nylon Cotton
Acetate Wool
Acrylic Mohair
Spandex Cashmere
Polyester


Fibers

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

Fibers

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


Fibers

Fiber Comparison

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

Fibers 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


Fibers

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


Fibers

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


Fibers

Synthetic Fibers
Made 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


Fibers

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.


Fibers

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


Fibers

Weave Patterns

•Basket
•Leno


Fibers

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

Fibers

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.
Characteristics:
Very strong
dense and compact
different faces;
diagonal design on surface

Fibers

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

Fibers

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


Fibers

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


Fibers

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.


Fibers

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.


Fibers

Filament Cross Sections

Round 4-lobed

Octalobal
Trilobal
Irregular

Dogbone or Multi-lobed
Dumbbell or Serrate

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.


Fibers

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


Fibers

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


Fibers

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


Fibers
Using Refractive Index


Fibers

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.


Fibers

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.


Fibers

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.


Fibers

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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Fibers