trace_evidence by niusheng11

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									Trace Evidence
Hair and Fibers
   Jennifer Hansen
Forensic Examination of Hair
   It is not yet possible to definitively match
    hair top one individual, but partial success
    has been achieved by isolating and
    characterizing the DNA
Hair Examination includes
   Color
   Structure
   Morphology
   DNA extraction, isolation, and
What is hair?
   Appendage of skin that grows out of an
    organ called hair follicle
   3 Layers of hair
       Cuticle- scale structures covering the exterior of
        the hair
       Cortex- Main body of hair shaft
       Medulla- Cellular column running through center
        of hair

   Resists chemical decomposition
   Retains structural features over a long
    period of time

   Human   vs.   Dog
   The main body of the hair shaft
   Comprised of spindle shaped cortical cells
    aligned in a regular array parallel to the
    length of the hair
   It contains pigment granules which gives
    hair its color
   Color, shape, and distribution of granules
    give hair its color
   A collection of cells that look like a central
    canal running through a hair
   The diameter of the medulla can help
    identify the species
   Humans medulla only accounts for 1/3 of
    interior of hair. Most animals over 50%
   The presence and appearance of the
    medulla vary from individual to individual
    and even among the hairs of an individual
Medulla can be …
   Continuous
   Interrupted
   Fragmented *
   Absent*
Continuous Medullae rare
   Most often seen in Asian races
   Shape and size of hair root determined by
    the growth phase
3 Phases of hair growth
   Anagen- Initial growth phase during which
    hair is actively produced can last 6 years
    Root is attached to follicle If hair pulled in
    this stage it may have follicular tag (DNA)
   Catagen- transition phase 2-3 weeks. Slow
   Telogen- Final growth phase in which hair
    naturally falls out of skin 2-6 months
Hair comparison
   Animal vs human
   May be used in conjunction with other
    evidence to link suspect to crime scene
Comparison of hair
   Color
   Length
   Diameter
   Presence/absence pattern of medulla
   Color intensity of granules

*** All of these can vary within an individual which
   makes it difficult to use as anything but class
Dyed & Bleached Hair
   Dyed hair present in cuticle and cortex
   Bleaching removes pigment from hair
   One can estimate time since last dye job
    knowing hair grows 1cm / month
Other defining characteristics
   Certain diseases deficiencies and
    medications can alter hair growth
   Presence of fungal and knit infections
Microscopic Examination of hair
   Comparison microscope best for side by
    side image
   11% Error found when matched visual
    samples did not match genetically
   Visual examinations are presumptive
Hair origin from body
   SCALP HAIR-little diameter variation,
    uniform distribution of pigment
   PUBIC HAIR- Short, curly, wide variation in
    diameter, continuous medullae
   Beard hairs- coarse, triangular in cross
    section . Blunt tips from shaving
Determination of race
   Caucasian- straight or wavy. Fine coarse
    pigments. Cross section= oval & round
   African Descent- kinky, dense unevenly
    distributed pigments Cross section= flat or

   Must be cautious! These are generalities!
Age or sex Determination
   Only infant hair is distinguishable
   If DNA can be obtained by root structure
    sex can be identified.
Can one tell if hair was forcibly
   Yes- if there is presence of follicular tissue
    (root sheath cells)
   The faster hair is removed the more likely
    one is to find these cells
Why is DNA processing difficult?
   High success rate of find DNA in root
    sheath cells that are forcibly removed
   Most DNA found is mitochondrial which can
    only be linked to heritage
Collection and Preservation
   50 full length scalp hairs + 24 full length
    pubic hair makes a decent sample size
   If victim of rape the pubic area must be
    combed before sample take to remove
    loose foreign hair. Foreign hair and comb
    are also collected in a separate envelope
Examination of Fibers
   Cross transfers from
       Homicide
       Assault
       Sexual offenses
       Hit and run victims
       Breaking and entering threads can be found in
        glass fragments and screens
Types of fibers
   Natural- wool, cashmere, mink, rabbit,
   Manufactued- rayon, nylon, polyester,
    acrylic, PBI, spandex, Acetate, Aramid,
    Bicomponent, lyocell, melamine,         I’m a
    modacrylic, olefin

Synthetic Fibers
   Fabric made completely by chemical
       Use of polymers- large number of atoms that are
        arranged in repeating units
   Plastics
   Paints
   Adhesives, synthetic rubber
   Smallest unit of an covalently bonded
   Multiple molecules linked together. High
    molecular mass.
   Long chain of repeating molecular units
       Each repeating chains is called monomer.
Identification and Comparison
   Some fabrics can be fitted together
   Usually a comparison microscope is used
    for small fibers
   Scientist looks for similarities in:
       Color
       Diameter
       Lengthwise striations
       Cross section
Analytical techniques
   Microspectrophotometer- the linking of a
    microscope and a spectrometer
       Compares color of fiber
       Small sample size 1 ml or less needed
   Chromatography- use solvent to remove dye and
    place dye on chromatography plate
   Infrared Absorption- can put fiber in selective
Significance of fiber evidence
   No way to rate how unique fiber is
   Helps mount circumstantial evidence
Collection and Preservation
   Clothing must be place in individual bags
   Carpet, rugs bedding
   Tape lift
   Forceps

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