Forensics Fiber Test
What is used to identify and compare fibers?
- Fourier Transform Infrared analysis (FTIR) - Optical microscopy - Pyrolysis gas chromatography-mass spectrometry (PGC-MS)
What are the problems with fiber evidence?
- class characteristic - the less common the fiber the more useful it is to identify a suspect
Why are fibers used to reconstruct crime scenes?
- condition of the garment/fiber - type and composition of the fabric - mobility of victim - length of time between actual and physical contact
What are fibers?
- considered class evidence - have probative value - common trace evidence at a crime scene - can be characterized based on comparison of both physical and chemical properties
What are individual characteristics of fibers?
- high probability of linkage with only one individual - one of a kind, unusually made fiber made in very small amount with unusual dye
What are the tests for identification?
- microscope observation - burning - thermal decomposition - chemical tests - density - refractive index - fluorescence
What are the basic comparisons of fiber samples?
- microscopic comparison of color and diameter - lengthwise striations - cross-section of fiber (shape) - fabric comparisons (weave pattern, thread count) - color separation
What are the types of synthetic fibers?
- rayon - nylon - acetate - acrylic - spandex - polyester (Under Armor) - polypropylene (bicycling clothing) - kevlar - lycra
What are the types of natural fibers?
- silk - linen - angora - cotton - wool - mohair - cashmere - hemp - all furs
What is the value of fibers dependent on?
- type of fiber - color or color variations in fiber - location of fiber - number of fibers that matches between victim and suspect
What are the classifications of natural fibers according to their origin?
- vegetable or cellulose - animal or protein - mineral
When was Williams convicted?
1982
What are the types of carpet fibers?
Orlon, Dacron
In what case did fibers weigh heavily on the outcome of the case?
Wayne Williams
What is fluorescence?
absorption and reemission of light; used for comparing fibers as well as spotting fibers for collection
How is the fiber from a scene compared to fiber from a known source?
all the characteristics found on the known fiber and the questioned fiber must be identical
What is wool?
animal fiber coming most often from sheep, but may be goat (mohair), rabbit (angora), camel, alpaca, llama, vicuna
What is a natural fiber?
animal, vegetable, or inorganic
What is FTIR?
based on selective absorption of wavelengths of light
What is cotton's value in forensic investigations?
basically meaningless
Why are fibers class evidence?
because of mass production of goods/garments
What is PGC-MS?
burns a sample under controlled conditions, separates and analyzes each combustion product
How are knitted fabrics made?
by interlocking loops into a specific arrangement
What is the second significance of fiber evidence?
can prove contact between an individual and an object
What is the first significance of fiber evidence?
can prove contact between two individuals
What was his conviction based on?
carpet fibers that were found in his home, car and on several murder victims
What is cellulose acetate?
cellulose chemically-altered to create an entirely new compound not found in nature
What does the design of plain weave resemble?
checkboard
What is rayon?
chemically-altered cellulose; soft, lustrous, versatile
What is used to separate dyes for comparative analysis?
chromatography
What does it mean to say fiber from a scene and fiber from a known source are similar fibers?
class or individual
What are class characteristics of fibers?
consistent with a group
A forensic scientist can only say that two fibers are what?
consistent with each other
What is yarn?
continuous strand of fibers or filaments, either twisted or not
Loops may be one _____ thread or a _____.
continuous, combination
What is a very common fiber?
cotton
Likelihood of finding transferred fibers on the clothing of the suspect _____ after each day that passes.
decreases
What are the individual qualities of the different fabrics?
degree of: - stretch - absorbency - water repellence - softness - durability
What is one of the most common examples of twill weave?
denim
What weave pattern does twill weave make?
diagonal weave pattern
What do you have to make sure when collecting fiber evidence?
different items are not placed on the same surface before being bagged
By varying the chemical structure of the monomers or by varying the way they are joined together, polymers are created that have _____ _____.
different properties
What is spandex?
extreme elastic properties
What is blend?
fabric made up of two or more different types of fibers
True or False - The holes of the nozzle are round.
false - not necessarily round
What is fabric made of?
fibers
What happens when synthetic fibers are hot?
forced out of a nozzle then woven
What is thermal decomposition?
gently heating to break down the fiber to the basic monomers
The way a fabric accepts a particular dye may also be used to do what?
identify and compare samples
In fabric production, what are fabrics composed of?
individual threads or yarns, made of fibers, that are knitted, woven, bonded, crocheted, felted, knotted or laminated
How do you bag clothing items?
individually in paper bags
What is silk?
insect fiber that is spun by a silk worm to make its cocoon; fiber reflects light and has insulating properties
What are polymers?
long chains of repeating chemical units
What does satin weave create?
long floats
How do you lift fiber evidence?
make tape lifts of exposed skin areas of bodies and any inanimate objects
What is fiberglass?
manufactured inorganic fiber
What is rock wool?
manufactured mineral fiber
What does the word polymer mean?
many (poly) units (mer)
What is density?
mass of object divided by the volume of the object
What is refractive index?
measurement of the bending of light as it passes from air into a solid or liquid
What are the repeating units of a polymer called?
monomers
How many different dye formulations are there?
more than 7000
What is nylon?
most durable of man-made fibers; extremely light weight
What is polyester?
most widely used man-made fiber
What are the types of fibers and fabric?
natural and artificial
What is asbestos?
natural fiber that has been used in fire-resistant substances
What is burning?
observation of how a fiber burns, the odor, color of flame, smoke and the appearance of the residue
What is secondary transfer?
occurs when already transferred fibers on the clothing of a suspect transfers to clothing of a victim
What is primary transfer?
occurs when fibers are transferred from a fabric directly onto a victim's clothing
Interlacing weave of satin pass _____ _____ or more yarns.
over four
The warp yearn of twill weave is passed _____ _____ to _____ weft yarns before going _____ one.
over one, three, under
What should fibers be stored in?
paper bag
What is the simplest and most common weave pattern?
plain weave
What are synthetic fiber made of?
polymers
What is important for the reconstruction of crime scene?
primary and secondary transfer
What is acrylic?
provides warmth from a lightweight, soft and resilient fiber
Yarn is formed into successive _____ of _____ then drawn through another _____ of loops to make the fabric.
rows, loops, series
What is the most obvious example of satin weave?
satin
Components that make up dyes can be _____ and _____ to an _____.
separated, matched, unknown
What should removed fibers be folded into?
small sheet of paper
What are chemical tests?
solubility and decomposition
What does the design of twill weave resemble?
stair steps
What is an artificial fiber?
synthesized or created from altered natural sources
What happens because the holes of the nozzle are not necessarily round?
the fiber may have a unique shape in cross-section
As a result of differences in polymers, what happens forensically?
they can be distinguished from one another
How can fiber evidence in court cases be used?
to connect the suspect to the victim or to the crime scene
True or False - It would take very unusual circumstances to be able to say that fibers had individual characteristics.
true
True or False - Most fabrics are either woven or knitted.
true
What are fibers made of?
twisted filaments
What must control samples of fibers be?
uncontaminated, large enough to do testing needed
The warp and weft yarns of plain weave pass _____ each other _____.
under, alternately
For satin weave, the yarn interlacing is not _____.
uniform
What is optical microscopy?
uses polarizing light and comparison microscopes
What is the third value of fiber evidence?
value is dependent
What is cotton?
vegetable fiber; strong, tough, flexible, moisture absorbent, not shape retentive
Where do control samples of fibers come from?
victims and suspects' homes and vehicles
What is the difference between warp and weft?
warp - lengthwise yarn weft - crosswise yarn
The more movement, the more likely fibers _____ _____ _____.
will be transferred
