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EVIDENCE found at the Crime Scene

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Presentation on theme: "EVIDENCE found at the Crime Scene"— Presentation transcript:

1 EVIDENCE found at the Crime Scene
Hair and Fiber Evidence

2 Evidence… 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 HAIR 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 Parts of Hair 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 Parts of Hair 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 Parts of Hair

7 Animal vs. human Medulla
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 Medulla of various species
Various medulla patterns appear in different species of animals

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

10 FIBERS 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 Fiber Sources 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 Fiber Evidence 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 Natural Fibers 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 Man-Made fibers 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 Synthetic fibers 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 Fiber Color 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 Collecting hair and fiber evidence
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 Fiber Analysis 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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