Monday 12/9/13
• AIM: how are fibers used in Forensic Science
• DO NOW: Explain how fiber analysis was a key to
the Wayne Williams trial and conviction.
• Motivation: Use a hand lens to analyze the fibers
on your sleeve. List any distinct characteristics
you observe.
• HW: Textbook read pages 159-160 Answer the
following:
– Should the press have free access to information turned up in the
course of an investigation? Why or Why not?
– Should fiber evidence be sufficient for a conviction when there is
not motive or witness testimony?
Can you identify the animal hairs shown?
Think About It …
(1)In which samples are we viewing the cuticle? How do they compare?
(2) In which samples are we viewing the medulla? How do they compare?
(3) What characteristics can be used to identify hair samples?
Types of Animal Hairs - Key
A
Dog or
Fox
B
Horse
C
Pig
D
Human
G
E
Deer
F
Rabbit
Cat
H
Deer
I
Human
Introduction and How Forensic Scientists Use
Fibers
•
How are fibers used in Forensic Science?
–
•
Fibers are not specific to an individual, but…
–
–
•
To create a link between crime and suspect or
to victim
often fall off and are picked up during activities
and go unnoticed
may provide police with evidence even if a
suspect wears gloves
Fibers are a form of trace evidence
–
Where can fibers originate?
4
Forensics of Fiber Analysis
What are fibers?
• The basic unit of fabrics
• Woven together to form fabric
• Besides hair, one of the most
common items left at a crime
scene
Explain how a forensic scientist
can connect a fiber found at a
crime scene to a suspect
Wednesday 12/11/13
• AIM: how do forensic scientist use fibers as
evidence?
• DO NOW: How can you tell the difference
between the two pictures below? How can
you compare them?
Why are dead bodies removed in
plastic bags instead of cotton
sheets?
What are fibers?
• Difficult to trace back to manufacturer
• Class evidence
• Statistics and probability can narrow down the
source (place it came from)
Fibers
 Can be characterized based on
comparison of both physical and
chemical properties
 The type and length of fiber used
 the type of spinning method
 the type of fabric construction all affect
the transfer of fibers and the significance
of fiber associations.
11
How do fibers make up fabric?
• Fibers aligned into a yarn (thread)
• Yarn is then weaved, knitted, crocheted, knotted, braided
etc. into a fabric
The three basic weaving patterns
PLAIN
TWILL
SATIN
Fabric
 A fiber can be spun with other fibers to form a
yarn that can be woven or knitted to form a
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
13
Kendall/Hunt Publishing Company
Fabric Production
• The degree of stretch, absorbency, water
repellence, softness and durability are all
individual qualities of the different fabrics.
14
Kendall/Hunt Publishing Company
SPIDER SPINNERETS
Why is the weaving pattern of interest to
forensic scientists?
• Each type of fabric has its own characteristics which can be
discovered by performing different tests
• Can tell what material may have been used during a crime
How do fibers end up at a crime scene?
•
Fiber Transfer
Direct Transfer
Secondary Transfer
Transfer occurs from Transfer occurs from
victim to suspect or a source to the
suspect to victim
victim then to the
suspect
Give an example of
this.
Give an example of
this.
Fiber Evidence
• Matching unique fibers on the clothing of a victim to
fibers on a suspect’s clothing can be very helpful to an
investigation
• whereas the matching of common fibers such as white
cotton or blue denim fibers would be less helpful.
• The discovery of cross transfers and multiple fiber
transfers between the suspect's clothing and the victim's
clothing dramatically increases the likelihood that these
two individuals had physical contact.
Forensics of Fiber Analysis
• Cross transfers of fiber often occur in cases in which
there is person-to-person contact
• Investigators hope that fiber traceable back to the
offender can be found at the crime scene, as well as
vice versa.
• Success in solving crimes often hinge on the ability to
narrow the sources for the type of fiber found, as the
prosecution did with their probability theory on the
fibers
Fiber Number
• The number of fibers on the clothing of a
victim identified as matching the clothing of a
suspect is important in determining actual
contact.
• The greater the number of fibers, the more
likely that contact actually occurred between
these individuals
Assessment
• The fiber below was found on the body of a
murder victim. As the forensic scientist
explain how you would analyze this fiber and
how it would help in solving the murder.
Fiber Evidence
• Fibers are gathered at a crime scene with
tweezers, tape, or a vacuum.
• They generally come from clothing, drapery,
wigs, carpeting, furniture, and blankets.
• For analysis, they are first determined to be
natural, manufactured, or a mix of both.
Wednesday 12/18/13
• AIM: How do forensic scientists identify
natural fibers?
• DO NOW:What is weaving pattern and why is
it important to the forensic scientist?
• HOMEWORK: Text read pages128,131-133.
answer questions 7-10 on page 162
Weaving pattern helps individualize
the fiber
• Each type of fabric has its own characteristics
• Can tell what material may have been used during a crime
Fiber and Textile Evidence
• The most common fiber transfer is
shedding of textiles (clothing, carpets,
upholstery)
• Fibers can be classified as:
– Natural Fibers (come from animals, plants,
and minerals minded from the ground)
– Synthetic Fibers (are man mad and are either
regenerated or polymers)
Types of Fibers
Synthetic






Rayon
Nylon
Acetate
Acrylic
Spandex
Polyester
Natural





Silk
Cotton
Wool
Mohair
Cashmere
Forensic Fiber Analysis
Why would this information be valuable to a forensic scientist?
• The world produced
approximately 80 billion
pounds of fabric in 1995,
about half of which was
cotton
• The other approximately
44 billion pounds of fiber
were manufactured or
synthetic.
Table 1.
U.S. Annual Production for Manufactured Fibers:
1995
(millions of pounds)
Fiber
Polyester
Product
3,887
Nylon
270
Olefin
521
Rayon/Acetate/Triace
tate
498
Acrylic/Modacrylic
432
(Table 1 [6]). All these fibers were used in a
variety of applications including but not
limited to clothing, household textiles,
carpeting, and industrial textiles.
Forensic Fiber Analysis
• It could be argued that the large volume of fibers
produced reduces the significance of a fiber
association discovered in a criminal case.
• Considering the volume of textiles produced
worldwide each year, the number of textiles
produced with any one fiber type and color is
extremely small.
• The likelihood of two or more manufacturers exactly
duplicating all of the aspects of the textile is
extremely remote
Classification
Natural fibers are classified
according to their origin:
 Vegetable or cellulose
 Animal or protein
 Mineral
Fiber
Classification
—Natural Fibers
Plant fibers:
•
Cotton from seedpods is the plant fiber most commonly
used in textiles (shown above).
•
Coir from coconuts is durable.
•
Hemp, jute, and flax from stems grow in bundles.
•
Manila and sisal from leaves deteriorate more quickly.
Mineral Fibers:
•
Fiberglass is a fibrous form of glass.
•
Asbestos is a naturally occurring mineral with a crystalline
structure.
34
Fiber Classification
—Natural Fibers
Plant fibers (made of the polymer cellulose):
• can absorb water.
• are insoluble in water.
• are very resistant to damage from harsh
chemicals.
• can only be dissolved by strong acids.
35
Cellulose Fibers
Cotton
• The most prevalent
plant fiber
• Cotton has a distinct
ribbon like shape with
twists at irregular
intervals
• Individual
characteristics such as
the type of cotton, fiber
length, and degree of
twist are compared
Other plant fibers
• Flax (linen), ramie, sisal,
jute, hemp, kapok, and
coir.
• The identification of less
common plant fibers at a
crime scene or on the
clothing of a suspect or
victim would have
increased significance.
Flax fibers viewed with
polarized light
Flax (linen)
Hemp
Pd 5 Thursday 12/19/13
Protein Fibers
 Wool—animal fiber coming
most often from sheep, but
may be goat (mohair), rabbit
(angora), camel, alpaca,
llama, vicuna
 Silk—insect fiber that is spun
by a silk worm to make its
cocoon; fiber reflects light and
has insulating properties
Silk
Assessment
• Explain how you could easily identify a plant
vs and animal fiber
Thursday 12/19/13
• Explain the difference between a natural and a
synthetic fiber
Animal Fiber: Wool
• Wool is the most
frequently used in the
production of textile
materials
• and the most common
wool fibers originate from
sheep.
• Finer woolen fibers are
used in the production of
clothing
• coarser fibers are found in
carpet.
• Fiber diameter and degree
of scale protrusion of the
fibers are other important
characteristics.
Wool fibers
Wool
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
Fiberglass
Rockwool
Asbestos
Fiber Classification
—Synthetic (artificially produced)
Fibers
• Until the nineteenth century only plant and
animal fibers were used to make clothes and
textiles.
• Half the products produced today are artificially
produced.
• Artificially produced fibers include rayon,
acetate, nylon, acrylics, and polyesters.
Forensic Science:
Fundamentals & Investigations,
Chapter 4
55
Fiber Classification
—Synthetic (artificially produced)
Fibers
Regenerated Fibers (derived from cellulose):
•
•
•
Rayon is the most common of this type of fiber. It
can imitate natural fibers, but it is stronger.
Celenese® is cellulose chemically combined with
acetate and is often found in carpets.
Polyamide nylon is cellulose combined with three
acetate units, is breathable, lightweight, and used in
performance clothing.
56
Fiber Classification
—Synthetic (artificially produced)
Fibers
Synthetic Polymer Fibers:
Petroleum is the basis for these fibers, and they have very
different characteristics from other fibers.
Monomers in large vats are joined together to form
polymers. The fibers produced are spun together into
yarns.
They have no internal structures, and under magnification
they show regular diameters.
Fiber Classification—
Synthetic
(artificially produced)
Fibers
spandex nylon
Examples of synthetic polymer fibers:
• Polyester—found in “polar fleece,” wrinkle-resistant, and not
easily broken down by light or concentrated acid; added to
natural fibers for strength.
• Nylon—easily broken down by light and concentrated acid;
otherwise similar to polyester.
• Acrylic—inexpensive, tends to “ball” easily, and used as an
artificial wool or fur.
• Olefins—high performance, quick drying, and resistant to wear.
Comparison of
Natural and
Synthetic Fibers
Visual Diagnostics of Some Common Textile Fibers
under Magnification
Forensic Science:
Fundamentals & Investigations,
Chapter 4
59
Fiber Evidence
• The problem with fiber evidence is that fibers
are not unique.
• Unlike fingerprints or DNA, they cannot
pinpoint an offender in any definitive manner.
• There must be other factors involved, such as
evidence that the fibers can corroborate or
something unique to the fibers that set them
apart.
Introduction and How Forensic Scientists Use
Fibers
•
Questions a forensic scientist will consider
when examining fiber evidence:
–
–
–
–
–
–
–
–
What type of fiber is it?
What is the fibers color?
Number of fibers found?
Where was the fiber found?
Textile the fiber originated from?
Are there multiple fibers transferred?
What type of crime was committed?
Time between crime and discovery of fibers?
Forensic Science:
Fundamentals & Investigations,
Chapter 4
62
Introduction and How Forensic Scientists Use
Fibers
•
In an investigation, collection of fibers
within 24 hours is critical.
–
•
Why?
Fiber evaluation can show such things as the
type of fiber, its color, the possibility of
violence, location of suspects, and point of
origin.
63
Sampling and Testing
•
•
•
•
Weaving spun fibers (yarns) together produces
clothing and many textiles.
Shedding from an article of clothing or a textile is the
most common form of fiber transfer.
Natural fibers require only an ordinary microscope to
find characteristic shapes and markings.
Infrared spectroscopy can reveal something of the
chemical structure of other fibers that, otherwise,
may look very much alike.
64
Sampling and Testing
•
How are fibers collected?
–
–
–
–
–
Special Vacuums
Sticky Tape
Forceps (tweezers)
Black Lights
Magnifying Glasses
65
Sampling
and Testing
• If a large quantity of fibers is found, some
can be subjected to destructive tests such
as burning them in a flame or dissolving
them in various liquids.
• Crimes can be solved in this way by
comparing fibers found on different
suspects with those found at the crime
scene.
66
Summary of Steps of Fiber Analysis
• In short, the fiber analyst compares shape,
dye content, size, chemical composition, and
microscopic appearances, yet all of this is still
about "class evidence.“
• Even if fibers from two separate places can be
matched via comparison, that does not mean
they derive from the same source, and there is
no fiber database that provides a probability
of origin.
Microscopic Examination
• A compound microscope uses light reflected from the surface
of a fiber and magnified through a series of lenses,
• The comparison microscope (two compound microscopes
joined by an optical bridge) is used for more precise
identification.
• The phase-contrast microscope, reveals some of the structure
of a fiber.
• Electron microscopes either pass beams through samples to
provide a highly magnified image, or reflect electrons off the
sample's surface.
• A scanning electron microscope converts the emitted
electrons into a photographic image for display. This affords
high resolution and depth of focus.
Spectrometer
• The spectrometer, which separates light into
component wavelengths.
• every organic element has a uniqueness to its
constituent parts.
• By passing light through something to produce a
spectrum, the analyst can read the resulting lines,
called "absorption lines."
• That is, the specific wavelengths are characteristic of
its component molecules of the substance.
Micro-spectrophotometer
• This microscope locates minute traces or shows how
light interacts with the material under analysis.
• Linking this to a computerized spectrophotometer
increases the accuracy.
• The scientist can get both a magnified visual and an
infrared pattern at the same time, which increases
the number of identifying characteristics of any given
material.
Can you identify the types of fibers shown?
Think About It …
(1)Which samples are natural fibers?
(2) Which samples are synthetic fibers?
(3) What characteristics can be used to identify fiber samples?
Types of Fibers - Key
Acrylic Yarn
Cotton Yarn
Nylon Rope
Polyester Yarn
Rayon Rope
Wool Yarn