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Hair and Fiber Evidence.  Trace evidence is small pieces of evidence left behind at a crime  Locard recognized the usefulness of trace evidence in reconstructing.

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Presentation on theme: "Hair and Fiber Evidence.  Trace evidence is small pieces of evidence left behind at a crime  Locard recognized the usefulness of trace evidence in reconstructing."— Presentation transcript:

1 Hair and Fiber Evidence

2  Trace evidence is small pieces of evidence left behind at a crime  Locard recognized the usefulness of trace evidence in reconstructing crime scene as he is known to say “EVERY CONTACT LEAVES A TRACE”  Examples of Trace Evidence  Hair  Fibers  Soil  Paint  Glass  Writing samples  Gun shot residue, explosives, drugs The focus of our trace evidence lessons

3  A wide variety of crimes leave hair samples at the crime scene  Morphology CANNOT link hair to a single individual  However, it can be used as strong corroborative evidence placing an individual at a crime scene.  Hair is very stable evidence and is resistant to chemical decomposition, retaining structural features over a long period of time

4  Cuticle  Outside covering on hair  Scale pattern is a useful CLASS characteristic  The variety of patterns formed by animal hair makes it important in species identification  Imbricate – found in all human hairs and some animals  Coronal –hair of small rodents (mouse, rats) and bats  Spinous – hair of minks, seals, and cats

5  Cortex  Pigment granules are in this section of the hair  Color, shape, and distribution of these granules provide the criminalist with important points of comparison among the hairs of different individuals

6  Medulla  Looks like a central canal running through the hair  In many animals, the medulla can be very wide, occupying more than half the hair’s diameter  For humans, the medulla usually less than 1/3 of the diameter  Its important to note that medulla can even vary between hairs on a single individual  Medulla patterns vary greatly with different animals (cat medulla resembles a strand of pearls and deer medulla looks like spherical cells occupying the entire center of the hair strand

7 Unisereal – cat or rabbit Lattice- deer, elk, goat Vacuolated – dog, red fox, cattle Multisereal – rabbit, chinchilla Amorphous – human continuous – black hair fragmented – all other hair

8  Various medulla patterns appear in different species of animals

9 Rounded root – hair lost naturally Spade shaped root – most likely dog Frayed root – most likely cat Follicle attached – hair pulled out Blackened Root – hair lost after death Wine-glass shaped root – most likely deer

10  Types  Natural fibers (animal or plant)  Man-made fibers  Synthetic fibers  Polymers Fibers are spun into yarn which can then be knitted or woven into fabrics

11  Fibers left at the crime scene can be matched by class characteristics to fibers relating to the suspect  It is more likely to be able to find a fiber (or hair) on a piece of evidence or known source that is immobile  Fibers may come from wigs, carpet, drapery, furniture, blankets, etc.  The more fibers found, the more likely that the evidence made direct contact with the source of the fibers

12  The fewer number of possible sources, the more evidentiary value they have  Databases with fibers exists to compare unknown samples to  When comparing fibers, analysts are comparing the type of fiber, the way it was woven, and its color  While billions of tons of fabric are produced, duplicating the fiber/yarn and its exact color are not too likely

13  Derived entirely from animal or plant sources  Wool – sheep (most common animal fiber)  Cashmere – goats  Fur fibers such as mink, rabbit, beaver and muskrat  Identification depends solely on color and morphological characteristics  Most common is cotton – however, the length of the fibers, the twist of the yarn, and the dye may make a cotton fiber unique  Hemp (pictured) – viewed with polarized light  The fineness or coarseness of the fiber can give the analyst information about the end-point of the fabric (ie. fine wool is use in clothing, while coarse wool is used in carpets)

14  Increasingly replacing natural fibers in garments and fabrics  Man-made fibers can originate from natural fibers but can also be synthetic  Polyester and nylon are the most common types of man- made fibers  Examples  Acrylic  Nylon  Polyester  Rayon  Spandex

15  The shape of the cross- section of synthetic fibers may be unique to a particular manufacturer and only produced for a finite amount of time  Unusual cross-section can add to the uniqueness of the fiber and therefore add to its evidentiary value Cross-sectional views of nylon carpet fibers as seen with a scanning electron microscope (SEM)

16  Fabrics undergo several dying processes to get the desired color  Fibers may be dyed, and then yarns dyed, and fabrics dyed  Sometimes color is applied to the outside of the fiber like a “painted” style  How the color is applied, absorbed, and the particular color are all used as evidence  Any fading or discoloration can have increased evidentiary value

17  Hair and fiber evidence can be collected at a crime scene using tweezers, tape, or a vacuum  Where the evidence is found can add to its value

18  The fiber should first be analyzed using a microscope for type of fiber, length, color, diameter, cross-section, damage, crimp (using stereomicroscope)  Microscopes useful: stereomicroscope, comparison microscope, and compound light microscope (with polarized light capability)  A side-by-side comparison of the fiber to a known fiber (if and when it become available) should be done (using a comparison microscope)  Chromatography can be used to analyze the components of the color of the fiber (destructive!)  Pyrolysis gas chromatography can be used to determine the type of an unknown fiber (destructive!)  Infrared Spectroscopy (IR) can be used to determine the type of fiber (synthetic – organic only) ** finding no fibers does not mean that no contact occured


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