1. Fiber Evidence
NOTE: Fabric is the type of material and fibers are the
“threads” that make up the fabric
The use of fiber evidence in court cases is used many times to connect the suspect to the victim or to the crime scene. In the case of Wayne Williams, fibers were the entire case. Williams was convicted in 1982 based on carpet fibers that were found in his home, car and on several murder victims. Although this case is unusual, fibers are generally considered of greater value as evidence than that of rootless hairs since they may contain a greater number of variables, thus showing more individual characteristics.

2. Polymers The word polymer means many (poly) units (mer).
Synthetic fibers are made of polymers which are long string of repeating chemical units.
The repeating units of a polymer are called monomers.
By varying the chemical structure of the monomers or by varying the way they are weaved together, polymers are created that have different properties.
As a result of these differences, forensically they can be distinguished from one another.

3. Analysis of Fibrous Material
U.S. Department of Justice
FBI, April 1999

4. 1. Classification Synthetic fibers Natural fibers:
Classified according to their origin:
Synthetic fibers
Natural fibers:
Vegetable or cellulose
Animal or protein
Mineral

5. Types of Fibers Synthetic Natural Polyester Rayon Nylon Acetate
Acrylic
Spandex
Natural
Silk
Cotton
Wool
Mohair
Cashmere
Angora

6. Cellulose Fibers
Cotton--vegetable fiber. Strong, tough, flexible; moisture absorbent; not shape retentive
Ramie--vegetable fiber. Less flexible than cotton so its often blended with cotton
Rayon--first man-made fiber; soft, lustrous, versatile fiber
Cellulose esters--cellulose is chemically altered to create an entirely new compound not found in nature.
Acetate--less expensive, less polluting than rayon

7. Can you tell the difference(s) between the cotton on
Fiber Comparison
Can you tell the difference(s) between the cotton on
the left and the rayon on the right?

8. Petroleum Plastics (Made from derivatives of petroleum, coal and natural gas)
Nylon--most durable man-made fabric; extremely light weight
Polyester--most widely used man-made fiber
Acrylic--provides warmth from a lightweight, soft and resilient fabric
Spandex--extreme elastic properties

9. Protein Fibers
Wool--animal fiber coming most often from sheep but may be goat (mohair), rabbit (angora), camel, mink, beaver
Silk--animal fiber that is spun by a silk worm to make its cocoon; fiber reflects light and has insulting properties
Wool Fibers (400X)

10. Mineral Fibers
Asbestos--a natural fiber that was used in fire-resistant substances
Metallics (mylar)--a manufactured mineral fiber
Fiberglass--another manufactured mineral fiber

11. 2. 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.
The degree of stretch, absorbency, water repellence, softness and durability are all individual qualities of the different fabrics.

12. Woven Fabric
Woven fabric are made by interlacing warp (lengthwise) and weft (filling) yarns. Warp run the length of the fabric and parallel to the selvage which is the edge of the fabric. Weft cross over and under the warp threads.
Types include:
Plain
Twill
Satin

13. Woven Fabric PLAIN 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

14. Woven Fabric
TWILL
Create by passing the warp yearn over one to two weft yearns before going under two
Makes a diagonal weave
Design resembles a stair steps
Denim is the most obvious example

15. Woven Fabric SATIN The yarn interlacing is not uniform
Creates long floats
Interlacing weave passes over four or more yarns
Satin is the most obvious example

16. Knitted Fabric
Knitted fabrics are made by interlocking loops into a specific arrangement. It may be one continuous thread or a combination. Either way, the yarn is formed into successive rows of loops and then drawn through another series of loops to make the fabric..
Diagram:

17. 3. Identification and Comparison of Fibers
Microscopic examination
Color--compositional differences in the dyes
Fibers surface--delustering particles that may be added by manufacturers
Microspectrophotometer--compares fiber colors through spectral patterns
Chromatography--gives a more detailed analysis of the dye composition

18. Identification and Comparison of Fibers (cont.)
Polarizing microscope
can be used to determine the refractive indices of various fibers. The fiber is immersed in a fluid that has a comparable refractive index. The disappearance of the Becke line is observed under the microscope.
In addition, fibers will absorb infrared light in a characteristic pattern. This can be observed through the use of an infrared microspectrophotometer and a scope.

19. Collection of Fiber Evidence
Bag 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.

20. Uniqueness Establishing Individual vs. Characteristics
If there is only one source for the transfer material with a controlled environment where the contact took place
If there is contamination of several different materials from surface onto surface two
If there is a method available to characterize the material, such as applying DNA
Otherwise, trace evidence would have only class characteristics.

21. Man, I was nailed when those forensic guys found
fibers from the kid’s math assignment in my teeth.