Fiber and Textile Evidence

Ms ClarkPVMHS

• 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. Type of fiber2. Fiber color3. Number of fibers found4. Where fiber was found5. Type of crime committed6. 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

Fiber Types• Textiles– 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