1. Fibers

2. 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

3. 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

4. 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)

5. FIBER CLASSIFICATIONS
Natural Fibers
Manufacutred

6. 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

7. Silk Factory

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

9. cashmere
llama
mink

10. wool

11. 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

12. 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.

13. Triacetate Fibers
Rayon Fibers
Acetate Fibers

14. MANUFACTURED FIBERS Synthetic Fibers
Produced solely from synthetic chemicals
nylons
polyesters
acrylics
Made of polymers: substances composed of a large number of atoms; these atoms are usually arranged in repeating units or monomers.

15. 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)

16. Jolliff Method

17. Jolliff Method

18. 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

19. 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.

20. Chromatography

21. 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.

22. 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

23. 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

24. 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

25. Robert Buell

26. Post Fiber Lab