Fiber Evidence

Fibers Example of Locard’s Exchange Principle –All garment surfaces have loose fibers that have been picked up through contact –Most common form of forensic evidence

Natural vs. Man-made Natural: Can be subdivided into: –Animal –Vegetable –Mineral Man-made: Manufactured (synthetic) –Began more recently –First showed up in WWII

Natural Fibers Animal -- All animal fibers are protein Vegetable -- Cellulose Mineral -- asbestos, mineral wool

Animal Fibers Wool: Can come from many different animals –Species-specific characteristics Shaved off animals and spun into threads May also be specific hairs (fur coats etc.)

Animal Fibers Silk: unraveled cocoon of a silkworm caterpillar Cocoons are boiled, unraveled and spun into the fibers

Vegetable Fibers Include cotton, linen, and bamboo May be dyed or undyed –Dyed is more helpful as dye can be analyzed Can be from seeds (cotton), fruit (coir) or stems (flax, jute, linen)

Mineral Fibers Primarily used for insulation Fiberglass: form of glass in short, brittle fibers Asbestos: naturally occurring mineral with long fibers

Man-made Fibers All are polymers –Repeating units of a monomer Includes polyester, nylon, acrylic, acetate Includes regenerated (start with natural materials) and synthetic (made from chemicals) fibers

Comparison of Natural and Synthetic Fibers FiberCharacteristics

Weave Patterns To weave, crosswise threads (weft) woven back and forth through lengthwise threads (warp) Pattern in which weft passes over and under warp is weave pattern Weave pattern can be used for forensic evidence

Fiber Evidence Scientists can use to identify origin of fiber or narrow possibilities If edges are torn and can be fit together, can show common origin Microscope analysis of fibers –Color –Shape: Cross-sectional, diameter –Striations on surface –Delustering particles to reduce shine

Fiber Cross-sectional Analysis

Fiber Identification Burn Test: –Approaching Flame: Melts, shrinks or curls away –In a Flame: Burns quickly, burns slowly, Does not burn at all Burning fibers may be self-extinguishing May give off distinctive odor –Residue: Ash-like, brittle, bead-like and hard

Fiber Identification Solubility: –Solvents include acetone, HCl and sodium hypochlorite –Some fibers completely dissolve –Some solvents may cause structural damage

Fiber Identification Staining: –Look at color and appearance –Different chemical nature of different fibers causes each to react differently to the staining mixture

Fiber Identification Microscopic appearance –Striations or smooth –Ribbon-like or cylindrical –Transparent or opaque

Collection and Preservation of Fiber Evidence Look for minute strands of fibers Relevant articles of clothing should be packaged carefully in separate paper bags Use clean forceps to remove fibers. –Place in small sheet of paper –Fold and label paper –Place paper packet inside another container