Fibers as Trace Evidence Fibers Fibers are EVERYWHERE
Fibers as Trace Evidence
Fibers • Fibers are EVERYWHERE! • As you interact with others or the environment, fibers become attached to your body and clothes, and drop off into the environment from your clothing, etc. ***What principle is this demonstrating? *** Locard’s Principle
What is a fiber? ? ? Fiber = the smallest unit of a textile material that has a length many times greater than its diameter. Using fibers to solve crime: https: //www. youtube. com/watch? v= bug. NBNVH 1 i 4
Fibers can be classified as: • 1 -Naturally occuring = found in nature (plants and animals) and not greatly altered in production –Examples: wool, silk, cotton, flax, hemp
2 - Manufactured or man made = originate from natural materials such as cotton or wood and undergo much processing (cellulose containing) --Examples: rayon (first man-made fiber) and acetate
3 -Synthetic = manufactured from synthesized chemical compounds (non-cellulose containing) --Examples: nylon, polyester, acrylic, etc
Fibers as Evidence • A fiber can be spun with other fibers to form a yarn that can be woven or knitted to form a fabric. • The type and length of fiber used, the type of spinning method, and the type of fabric construction all affect the transfer of fibers and the significance of fiber associations. This becomes very important when there is a possibility of fiber transfer between a suspect and a victim during the commission of a crime.
Fibers are everywhere. . . • Most textiles are mass produced. . . thus it is hard to trace a fiber to a specific source • Fibers can still be useful to create links among victims, suspects, and places. ***What type of evidence do we call this? ? *** Class Evidence
Interesting Points on Fibers. . . Cotton fibers are the plant fibers most commonly used in textile materials
The animal fiber most frequently used in the production of textile materials is wool, and the most common wool fibers originate from sheep.
More than half of all fibers used in the production of textile materials are man-made. Cross-section of a man-made fiber
Fabric Production 1. Fabrics are composed of individual threads or yarns that are made of fibers and are knitted, woven, bonded, crocheted, felted, knotted, or laminated. 2. Most are either woven or knitted. 3. The degree of stretch, absorbency, water repellence, softness, and durability are all individual qualities of the different fabrics.
Weave Terminology 1. Yarn—a continuous strand of fibers or filaments that may be twisted together 2. Warp—lengthwise yarn 3. Weft—crosswise yarn 4. Blend—a fabric made up of two or more different types of fibers
Weave Patterns
Plain Weave 1. The simplest and most common weave pattern 2. The warp and weft yarns pass under each other alternately 3. Design resembles a checkerboard
Twill Weave 1. The warp yarn is passed over one to three weft yarns before going under one. 2. Makes a diagonal weave pattern. 3. Design resembles stair steps. 4. Denim is one of the most common examples.
Satin Weave 1. The yarn interlacing is not uniform 2. Creates long floats 3. Interlacing weave passes over four or more yarns 4. Satin is the most obvious example
Knitted Fabric 1. Knitted fabrics are made by interlocking loops into a specific arrangement. 2. It may be one continuous thread or a combination. 3. The yarn is formed into successive rows of loops and then drawn through another series of loops to make the fabric.
Filament Cross Sections 1. Synthetic fibers are forced out of a nozzle when they are hot, and then they are woven. 2. The holes of the nozzle are not necessarily round; therefore, the fiber filament may have a unique shape in cross section. Round 4 -lobed Octalobal Trilobal Irregular Dogbone or Dumbbell Multi-lobed or Serrate
Using fibers to reconstruct crime scenes 1. The condition of the garment/fiber 2. The type and composition of the fabric. 3. Mobility of victim • The more movement, the more likely fibers will be transferred 4. The length of time between actual physical contact. • Likelihood of finding transferred fibers on the clothing of the suspect decreases after each day that passes. • https: //www. youtube. com/watch? v=Bj LHW 7 q. QEl 0
Testing for Identification 1. Microscopic observation 2. Burning — observation of how a fiber burns, the odor, color of flame, color of smoke, and the appearance of the residue 3. Thermal decomposition — gently heating to break down the fiber to the basic monomers 4. Chemical tests — solubility and decomposition
5. Density — the mass of an object divided by the volume of the object 6. Refractive index — measurement of the bending of light as it passes from air into a solid or liquid 7. Fluorescence — absorption and reemission of light; used for comparing fibers as well as spotting fibers for collection
Collection of Fiber Evidence 1. Bag clothing items individually in paper bags. Make sure that different items are not placed on the same surface before being bagged. 2. Make tape lifts of exposed skin areas and any inanimate objects. 3. Removed fibers should be folded into a small sheet of paper and stored in a paper bag.
Problems with Fiber Evidence 1. Class Characteristic • Mass production of goods/garments 2. The less common the fiber the more useful it is to identify a suspect. • Cotton: Very common – Basically meaningless in forensic investigations.
Basic Comparison of Fiber Samples 1. Microscopic comparison of color and diameter 2. Compare lengthwise striations 3. Compare cross-section of fiber (shape) 4. Fabric Comparisons (weave pattern, thread count). 5. Color separation
How can forensic scientists examine trace evidence? • Compare. . . physically. . . using microscopy. . . chemically.
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. 27
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