Fibers Another example of trace evidence Chapter 10: Fibers Another example of trace evidence

DEFINITION OF FIBER A fiber is the smallest unit of a textile material that has a length many times greater than its diameter. Fibers can occur naturally as plant and animal fibers, but they can also be man-made. A fiber can be spun with other fibers to form a yarn that can be woven or knitted to form a fabric. Fibers are usually collected from clothing, carpeting, furniture, beds, and blankets. Fibers are often important evidence in crimes that involve personal contact.

There are two types of fibers: natural and man-made (synthetic) Cotton Linen Wool Mohair Cashmere Silk Man-Made Polyester Rayon Nylon Acetate Acrylic Spandex

Types of Fibers Natural fibers are classified based on their origin. Three classifications Vegetable/Plant Animal Mineral

Cotton The most common plant fiber The wide-use of undyed white cotton in clothing and other fabrics has made this fiber meaningless as evidence. However, when the cotton is dyed with a combination of colors, the value as evidence is increased.

A Microscopic Look at Cotton A unique trait of cotton fibers is a ribbon-like twist at irregular intervals.

Linen Made from the skin of the stem of a flax plant. Linen fibers are used in clothing, lace and bed sheets.

Ramie, Jute and Hemp Also made from the skin of a plant stem, but processed differently from linen. These fibers are mainly used for rope. Growing of hemp has been banned in the U.S. since 1937 even though it only contains a trace amount of THC, grows faster and more hardy than cotton, and is one of the strongest and most durable fibers known.

Kapok Made from the seed pod of a tree found in Asia. These fibers are used as fillers for pillows, mattresses and toys.

Animal Fibers Animal fibers are the most common natural fiber found at a crime scene. These include: wool (sheep) mohair (angora goat) cashmere (cashmere goats) alpaca mink

These are animal hairs so you may notice the medulla and the cuticle. Wool The animal fiber that is most commonly used in textile materials is wool. The animal wool most commonly used is a sheep. Wool is used for clothing and carpet. These are animal hairs so you may notice the medulla and the cuticle.

Animal Fibers from Excrement Silk comes from the blind, flightless moth Bombyx mori. After the silkworm hatches, it eats mulberry leaves continuously for 6 weeks. Next, it secretes a clear fluid that hardens into a silk cocoon. This cocoon is separated into silk fibers.

A Microscopic Look at Silk Silk has a triangular structure that causes the silk fiber to refract incoming light at different angles. This refraction results in a shimmering, shining appearance.

A Mineral Fiber Asbestos is a naturally occurring silicate mineral that is composed of thin fibrous crystals. Asbestos has been used in building materials since the late 19th century. Asbestos has been identified as a carcinogen so use of this material is limited.

A Microscopic Look at Asbestos

Man-Made/Manufactured Fibers More than 50% of all textiles are created from man-made fibers. Two types Regenerated Synthetic

Regenerated Fibers Fibers are made from natural raw materials 1st made in 1911 was rayon Acetate is another regenerated fiber

Synthetic Fibers Synthetic fibers are polymers (also called macromolecules) composed of a large number of atoms arranged in repeating units known as monomers. 1st made in 1939 was nylon Also include polyesters, and acrylics. Most of the fibers manufactured today are synthetic **See Table 10-1 pages 369 & 370**

Fibers as Evidence Fibers may be exchanged between two objects or between an individual and an object. Whether or not a fiber is transferred is dependent on the type of fabric(s) involved the length of time of the contact .

Fibers as Evidence (cont) The cross-section of a man-made fiber is manufacturer specific. Some cross sections are more common than others. Unusual cross sections increase the value of the evidence.

Fibers as Evidence (cont) Fibers may be dyed before or after they are woven into a fabric. Dye may also be applied to the surface of a fabric. A dye’s color may be absorbed unevenly and may fade over time. All of these factors must be considered when trying to match a crime scene sample with a control/reference sample.

The Analysis of Fibers A Microspectrophotometer compares fiber colors through spectral patterns. Chromatography gives a more detailed analysis of the dye composition. Double Refraction determines the value of the refractive index of the fiber (how it bends light – contributes to shine of fabric) Infrared Spectrophotometry allows infrared analysis of a single strand of fiber while being viewed under the microscope

When the fibers become a fabric Fabrics are composed of individual fibers. These fibers may be knitted, woven, bonded, crocheted, felted, knotted or laminated. The method used to construct the fabric will determine the amount of stretch, absorbency, water repellence, softness and durability. These characteristics are unique to a fabric.

Woven Fabric Woven fabrics are made by interlacing the warp (lengthwise thread) and the weft (crosswise thread). The warp runs the length of the fabric and parallel to the selvage which is the edge of the fabric. The weft crosses over and under the warp threads. Types of weave patterns include: Plain Twill Satin

The Plain Weave Simplest and most common weave Warp and weft pass under each other alternately Create even patterns of 1/1 and 2/2 Design resembles a checkerboard

The Twill Weave Created by passing the warp thread over one to three weft threads before going under. Makes a diagonal weave Design resembles a stair step pattern Denim is the most obvious example

The Satin Weave The interlacing is not uniform Interlacing weave passes over four or more yarns Satin is the most obvious example

Knitted Fabric Knitted fabrics are made by interlocking loops into a specific arrangement. It may be one continuous thread or a combination of threads. The yarn is formed into successive rows of loops.

The Weave Pattern and Transfer A tightly woven or knitted fabric “sheds” less than a loosely woven or knitted fabric. Some textile materials such as leather do not transfer fibrous material. The age and condition of the fabric will affect the amount of fiber transfer. How often and for how long a fabric was manufactured is also important to an investigation.

Ripped Fabric If fabric evidence is ripped or torn, and both pieces are collected, the edges will be examined under a comparison microscope. The weave pattern must match.

Collection of Fiber Evidence Fibers that are visible and attached to an object should be photographed, drawn and described. Then the entire object should be packaged. If fibers are visible and loose they should be carefully removed with clean tweezers and packaged in a paper bindle.

The Wayne Williams Case The1979-1981murders in Atlanta, GA Wayne Williams case was solely based on hair and fiber evidence. The fibers were very unique in color and cross-sectional area. Williams continues to insist that he is innocent.

REFERENCES Ramsland, Katherine. "Fiber Analysis." Crime Library. 13 Mar 2008<http://www.crimelibrary.com/criminal_mind/forensics/trace/1.html>. "Masthead of Forensic Science Communications." Forensic Fiber Examination Guidelines. April 1999 Volume 1 Number 1. Federal Bureau of Investigation. 13 Mar 2008<http://www.fbi.gov/hq/lab/fsc/backissu/april1999/houcktoc.ht>. Lewin, Menachem, and Pearce. Handbook of Fiber Chemistry. New York: Marcel Dekker. "The Thin Blue Line." Forensic Scientists, Hair and Fibers. 13 Mar 2008 <http://www.policensw.com/info/forensic/forensic7a.html>. Carpet and Rug Fiber Chemistry. Bane-Clene Corporation 2007. 13 Mar 2008 <http://www.baneclene.com/articles/fiber-chemistry.html>.