Fiber and Textile Evidence
Ms Clark
PVMHS
• Fibers are used in forensic science to create a
link between crime and suspect
• If fibers from one person’s clothing were
found on a murder victim, does this
evidence prove that this person
committed the crime?
• Why or why not?
• Example:
– A thief owns a jacket made of a material
that happens to match the type of fiber
found at the crime scene.
• This does not mean that he was there, but a
jacket like his was.
• Example:
– A thief owns a jacket made of a material
that happens to match the type of fiber
found at the crime scene.
• This does not mean that he was there, but a
jacket like his was.
– If a jacket fiber, sock fiber, and shirt fiber all
from the items the thief owns are found at
the crime scene, then the chances they
were present are higher or increased.
What type of evidence are fibers?
•
•
•
•
Trace evidence?
Direct or circumstantial?
Class or Individual?
Physical or Biological?
What type of evidence are fibers?
• Trace evidence?
– Yes
• Direct or circumstantial?
• Class or Individual?
• Physical or Biological?
Fiber Transfer
• Direct transfer
– Fibers transferred directly from victim to suspect
or suspect to victim
• Secondary transfer
– Victim picks up fibers, then transfers them to
suspect
– Fibers are transferred from original source to
suspect and then to the victim or crime scene
Fiber Transfer
• Example of direct transfer
– Fiber from suspect’s shirt transfers onto victim
• Example of secondary transfer
– Fiber from carpet at suspect’s home transfers onto
his shirt, then transfers onto victim
Fiber Collection
• Early collection is critical
– Within 24 hours, an estimated 95% of all fibers
may have fallen from a victim or been lost from a
crime scene
• Only collect fibers that are unexpected
– Ex: Victim has a pink carpet at home, don’t collect
pink fibers
Considerations by Forensic Scientists
1.
2.
3.
4.
5.
6.
Type of fiber
Fiber color
Number of fibers found
Where fiber was found
Type of crime committed
Time between crime and discovery of fiber
• Using your book, elaborate on each of these
considerations and add to your notes
additional questions to follow up these initial
considerations.
Fiber Collection
• Special vacuums
• Sticky tape
• Forceps
– Important to be very accurate in recording where
fibers were found
– Incomplete or inaccurate recording may cause
evidence to be inadmissible in court
Fiber Analysis
• Identify type of fiber and
characteristics
– Color, shape
• Match to fibers from a suspect source
(car, home)
• If only one fiber is obtained, only tests
that will not damage or alter the fiber
can be used
– Polarizing light microscopy, infrared
spectroscopy
Fiber Analysis
• Polarizing Light Microscopy
– Allows scientist to observe fiber at specific
wavelengths
• Infrared spectroscopy
– Emits a beam that bounces off the material then
returns
– How the beam of light has changed reveals details
of the chemical structure of the fiber
Fiber Analysis
• If large quantities are obtained, some fibers
may be subjected to simple, but destructive
testing
– Burning in flame
– Dissolving in liquid
• Textiles
Fiber Types
– Most common form of fiber transfer
– Clothing, carpets, upholstery
– Constructed by weaving yarns
• Arranging lengthwise threads (the warp) then weaving
crosswise threads (the weft) into different patterns
– This is called the “weave pattern”
– Types of weave patterns: tabby, twill, satin
Weave patterns
• Using page 86 in your book, fill out your
“weave patterns” table.
• Draw a diagram of each one
Fiber Types
• Yarns
– Made up of fibers that have been “spun” together
– “Twist” direction is used as part of identification
Fiber Classification
• Natural fibers
– Come from animals, plants, minerals
• Synthetic fibers
– Man-made fibers
Natural Fibers
• Animal fibers
– 3 sources: hair, fur, webbing
– Made of proteins
– Ex: Fur coats, wool from sheep used in textiles, silk
• Plant fibers
– Specialized plant cells
– Sources: seeds, fruits, stems, leaves
– Made of cellulose
– Ex: Cotton
Plant Fibers
• Seed fibers
– Cotton is found at the seed of the cotton plant
• Fruit fibers
– Coir is a coarse fiber obtained from the covering of
coconuts
• Stem fibers
– Hemp, flax
• Flax is most common – found in linen
• Leaf fibers
– Manila is a fiber extracted from abaca leaves (relative of
banana tree)
– Other leaf fibers used to make ropes, twines, netting
Natural Fibers
• Mineral fibers
– Fiberglass
– Asbestos
Synthetic (man-made) Fibers
• Regenerated fibers (modified natural fibers)
– Derived from cellulose
– Mostly plant in origin
• Ex. Rayon
• Polymer fibers
– Originate from petroleum products
– Easy to distinguish between synthetic fibers in lab
• Ex: Polyester (found in fleece, wrinkle resistant clothes),
Nylon, Acrylic (imitation wool), Olefins (thermal socks
and carpets)
Natural vs Synthetic Fibers
• Synthetic fibers are stronger than natural
fibers
• Synthetic fibers are not damaged by
microorganisms
• Synthetic fibers can deteriorate in sunlight
• Synthetic fibers melt at lower temperatures
than natural fibers
Appearances of Common Fibers under
Microscope
• Using page 84, determine what fiber each
characteristic belongs to. Copy it down in your
table.
Summary
• Class evidence and trace evidence
• Scientists try to determine type of fiber, its
color, how many if each fiber were found,
what textile the fiber came from, whether
there were transfers of multiple types of fibers
• May be gathered using special vacuums, sticky
tape, or tweezers
Summary
• Analyzed using polarizing light microscopy,
infrared spectroscopy, burn tests, solubility tests
• May be natural or synthetic
• Natural: animal hair, plant fibers from seeds, fruit,
stems, or leaves, and mineral fibers
• Synthetic: Regenerated or modified natural fibers
and polymer fibers
• Spun into yarns with specific characteristics
• Yarns are woven into textiles with different
patterns