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, car and on several murder victims.

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.

Collection of Fiber EvidenceBag 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 of bodies and any inanimate objects

Removed fibers should be folded into a small sheet of paper and stored in a paper bag.

Fiber Collection

• 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.

FibersAre considered class evidenceCan be used as confirmationAre common trace evidence at a

crime sceneCan be characterized based on

comparison of both physical and chemical properties

Fabric

Fabric is made of fibers. Fibers are made of twisted filaments

Types of fibers and fabricNatural—animal, vegetable or

inorganic Synthetic/Artificial—synthesized or

created from altered natural sources

Types of Fibers

SyntheticRayonNylonAcetateAcrylicSpandexPolyester

NaturalSilkCottonWoolMohairCashmereLinen

ClassificationNatural fibers are classified according to

their origin:

Vegetable or cellulose Animal or protein Mineral

Cellulose Fibers Cotton—vegetable fiber; strong, tough,

flexible, moisture absorbent, not shape retentive

Rayon—chemically-altered cellulose; soft, lustrous, versatile

Acetate/Cellulose acetate—cellulose chemically-altered to create an entirely new compound not found in nature.

Animal/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

Mineral FibersAsbestos—a natural fiber that

has been used in fire-resistant substances

Fiberglass—a manufactured inorganic fiber

Synthetic Fibers(Made from derivatives of petroleum, coal and natural gas)

Nylon—most durable of man-made fibers; extremely light weight

Polyester—most widely used man-made fiber

Acrylic—provides warmth from a lightweight, soft and resilient fiber

Spandex—extreme elastic properties

Fabric Production

Fabrics are composed of individual threads or yarns, made of fibers, that are knitted, woven, bonded, crocheted, felted, knotted or laminated.

Most are either woven or knitted.

Weave Terminology

Yarn—a continuous strand of fibers or filaments, either twisted or not

Blend—a fabric made up of two or more different types of fiber.

Woven

The yarns pass under each other alternately

Design resembles a checkerboard

Weave Patterns

Knitted Fabric

Knitted fabrics are made by interlocking loops into a specific arrangement.

Filament Cross-Sections

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.

Use a microtome

Testing for IdentificationMicroscopic observation

Burning—observation of how a fiber burns, the odor, color of flame, smoke and the appearance of the residue

Testing for Identification - also Thermal decomposition

Chemical tests

Density

Refractive Index

Fluorescence

Dyes – both components that make up dyes and The way a fabric accepts a particular dye can be separated and matched to an unknown.

Microscopy• Fibers should be first examined with a

stereomicroscope (40X). Physical features such as crimp, length, color, relative diameter, luster, apparent cross section, damage, and adhering debris should be noted.

• Fibers are then tentatively classified into broad groups such as synthetic or natural AND woven or knit.

Side-by-Side Comparisons.• If all of the characteristics are the same

under the stereoscope, the next step is to examine the fibers with a comparison microscope.

• This side-by-side and point-by-point examination is the best technique to discriminate between fibers, especially those that appear to be similar.

• The physical characteristics of them must be compared visually with the comparison microscope to determine if they are the same in the known and questioned samples.

• Photography is recommended for later demonstration.

Summary of Fiber Analysis• In short, the fiber evidence 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.

Fiber Samples to be Examined

Natural•Cotton woven•Cotton knit•Silk•Linen •Wool

Synthetic• Polyester woven• Polyester knit• Rayon• Nylon• Acrylic• Satin