Fibers

Learning Objectives Understand the differences between natural and manufactured fibers List the properties of fibers that are most useful for forensic comparisons Describe the proper collection of fiber evidence

FIBER EVIDENCE Fibers may become important evidence in incidents that involve personal contact: homicide assault sexual offenses Similarly, the force of impact between a hit-and-run victim and a vehicle often leaves fibers, threads, or whole pieces of clothing adhering to parts of the vehicle Fibers may also become fixed in screens or broken glass during a breaking and entering attempt

Uses of Fiber at Crime Scene Vernon J. Gerberth, in Practical Homicide Investigation, points out that hair (and fiber) evidence is useful in: 1) Helping to establish the scope of the crime scene 2) Placing a perpetrator at a scene 3) Connecting a suspect with a weapon 4) Supporting witness statements 5) Connecting crime scene areas (abduction, vehicle used, dump site)

FIBER CLASSIFICATIONS Natural Fibers Manufacutred

NATURAL FIBERS Fibers derived entirely from animal or plant sources Animal Fibers constitute most of the natural fibers encountered in crime laboratory examinations. Forensic examination of animal fibers uses the same procedures discussed in the previous section on hair. Hair Coverings Sheep (wool), goats (mohair, cashmere), camels, llamas, alpacas, and vicuñas Fur Fibers Mink, rabbit, beaver, and muskrat Silk Silk worms, spiders Plant Fibers most prevalent is cotton

Silk Factory

The microscopic view of cotton fiber reveals its most distinguishing feature – a ribbon-like shape with twists at irregular intervals.

cashmere llama mink

wool

MANUFACTURED FIBERS Fibers derived from either natural or synthetic polymers Began with the introduction of rayon in 1911 and the development of nylon in 1939 Today they are marketed under 100’s of different trademark names Polyesters Dacron Fortrel Kodel Terylene http://www.fibersource.com/f-tutor/q-guide.htm

MANUFACTURED FIBERS Regenerated Fibers Fibers manufactured from natural raw materials (regenerated cellulose) rayon acetate triacetate For example, the first machine-made fibers were derived from cotton or wood pulp.

Triacetate Fibers Rayon Fibers Acetate Fibers

MANUFACTURED FIBERS Synthetic Fibers Produced solely from synthetic chemicals nylons polyesters acrylics http://www.youtube.com/watch?v=y479OXBzCBQ Made of polymers: substances composed of a large number of atoms; these atoms are usually arranged in repeating units or monomers.

Identification and Comparison of Manufactured Fibers Side-by-side microscopic comparison of control and crime-scene fibers Color and diameter there needs to be agreement between these two properties for there to be a possible match Lengthwise striations on the surface of the fiber The presence of delustering particles that reduce shine The cross-sectional shape of the fiber Cross-section of nylon (electron microscope)

Jolliff Method

Jolliff Method

Identification and Comparison of Manufactured Fibers Dye Composition Manufacturers use a mixture of dyes Analyze colors with a visible-light microspectrophotometer can use a sample as small as 1mm or less in length nondestructive technique (fibers remain intact) Process is carried out on fibers mounted on a microscope slide Analyze dye composition through chromatographic separation Extract dye off of fibers with a suitable solvent and analyze using a thin-layer chromatography plate

Microspectrophotometer An instrument that links a microscope to a spectrophotometer. The obvious advantage of this instrument is that the forensic analyst can view a substance through a microscope AND at the same time have the instrument plot the infrared absorption spectrum for the material. The IR spectrum is like a “fingerprint” for each chemical substance.

Chromatography http://www.youtube.com/watch?v=7tAVwF3IqW0

Fiber Evidence The quality of the fiber evidence depends on the ability of the criminalist to identify the origin of the fiber or at least be able to narrow the possibilities to a limited number of sources. Obviously, if the examiner is presented with fabrics that can be exactly fitted together at their torn edges, it is a virtual certainty that the fabrics were of common origin.

Fiber Evidence No analytical technique will permit criminalist to associate a fiber strand definitively to any single garment No databases are available for determining the probability of a fiber’s origin Nevertheless, one should not discount or minimize the significance of fiber evidence Forensic scientists compare color size shape microscopic appearance chemical composition dye content Read Significance of a Match on page 339. Unlikely that two indistinguishable colored fibers can come from randomly selective sources

Collection of Fiber Evidence Usually not seen with the naked eye, therefore can easily be overlooked The investigator’s task of looking for minute strands of fibers often becomes one of identifying and preserving potential “carriers” of fiber evidence. Time consuming and tedious Hunt and pick … need to get on hands and knees to look for this type of evidence Lifting Methods Clean forceps Adhesive tape lifts Gel lifters Use Lighting Aids Flashlights Ultra-violet lights

Packaging of Fiber Evidence relevant articles of clothing should be packaged carefully in paper bags each article should be placed in separate bags carpet, rugs, and bedding folded carefully car seats should be covered with polyethylene sheets knife blades should be covered to protect adhering fibers fibers removed from a surface should be placed inside a piece of paper, which is then folded and labeled and then put inside a second container label all packages

Robert Buell http://www.clarkprosecutor.org/html/death/US/buell801.htm

Post Fiber Lab http://www.youtube.com/watch?v=kb4tCcnA6jo