Trace Evidence
Part I
Trace Evidence ReviewA.Trace Evidence – refers to
minute (tiny) physical evidence that may be transferred between a perpetrator to a victim or to and from the crime scene
LEP!! B. The case of the gold coin counterfeiters!
Coins were being made illegally from brass alloys Three suspects were caught Each had tiny shavings of metal in coat
pockets Prisoner’s Dilemma!
Trace Evidence ReviewC. Types of Trace Evidence
1) Hair - animal or human
2) Fibers - textile products (sheets, rugs, clothing)
3) Soil
4) Botanicals - assorted plant parts including pollen
5) Glass – assorted sources
6) Paint – car in particular
7) Other – bits and fragments of materials
The Microscope – History
D. Historical notes1) 1590’s - Zacharias Janssen
☻ Dutch☻ Built first simple microscope☻ Actually jailed at one point for
counterfeiting
2) 1670’s - Anton Van Leeuwenhoek ☻ Dutch☻ Father of Microbiology☻ improved the construction of the simple
microscope ☻ magnification increased to 270x !!!
The Microscope – HistoryD. Historical notes
3) 1660’s - Robert Hooke☻ English☻ built first compound
light microscope☻ Drew huge numbers of
organisms using it!
4) 1920’s – Colonel Calvin Goddard☻ American☻ developed comparison microscope ☻ Used extensively in bullet
comparisons and firearm identification
E. Microscope terminologyMagnification ☻ to make an object appear bigger than it is☻ Use of the ocular and objective lenses gives total magnification ☻ total magnification = ocular x objective
low = 10 x 10 = 100 x high = 10 x 40 = 400 x
Resolution ☻ the clarity of an image or;☻ the ability to distinguish between two
objects very close together
Field of view (FOV) ☻ what you actually see in the ocular☻ inverse relationship between magnification and FOV☻ as magnification increases, FOV decreases☻ Size of FOV allow us to determine size of objects
F. Measurements Under the Microscope☻ Units of measure under the microscope
the micron (u) 1,000 microns = 1 millimeter Therefore, 500 microns = ?? ________ And 2,000 microns = ?? _________
☻ The FOV allows us to determine relative size under the microscope
☻ Example In the ocular… a hair of unknown width But we know the width of the FOV is
1,000 microns The hair covers half the FOV What is the width of the hair?
F. Measurements Under the Microscope1. What is the width of the hair if the hair covers 1/5
of the FOV (FOV = 800 u)?
2. What is the size of a hair if the hair covers 1/6 of the FOV (FOV = 240 u)?
3. In question 2, if the magnification shown is high power (400x), what is the FOV under low power (100x)?
Standard Compound Light Microscope☻ typical
“biological” scope
☻ used for Hair, fibers Blood and
tissue
☻ medium magnification (40x – 1,000x)
G. Types of Microscopes
G. Other Types of Microscopes
2. Stereomicroscope “workhorse” of crime lab Two eye pieces provides 3-D image used to view most evidence as a preliminary
check low magnification (10x - 60x)
3. Polarized Light Microscope uses polarizing light filters (glorified ray bans) shows birefringence - double bending of light used in examining soil, synthetic fibers, and glass medium magnification (40x – 1,000x)
G. Other Types of Microscopes
4. Comparison Microscope one ocular but double objective lenses allow two objects to be compared and matched in one
FOV especially useful in firearms analysis low to medium magnification (10x – 1000x)
5. Electron Microscope uses a beam of electrons instead of a beam of light detectors in device produce an image magnification up to 100,000x
Hair☻Function
an appendage for maintaining warmth
Found on various body parts
☻Structure Composed of a material called keratin Cuticle
• a protective outer coating • composed of units called scales
Medulla• an inner air space• may be filled with cells
Cortex• composed of microfibers (very thin protein tubes) • surrounded by protein
Trivia – the curlier the hair, the more sulfur bonds in it
H. Hair Evidence
Other Notes on Hair Structure
☻Cuticle Different species have
different scale patterns
☻Medulla an inner air space, may
be filled with cells Four forms of medulla
• Trace• Continuous• Discontinuous • Absent
Dog
Mouse
Cat
Other Notes on Hair Structure☻Hair Growth Anagenic phase
• growing phase of hair• Hair grows 1 mm per day on
average• A history of your drug use!!!• Pulled hair looks ragged• Shows signs of struggle
Telogenic phase• The dormant phase• Hair can easily be pulled out at
this point • Root is club shaped in humans
Other Notes on Hair Structure☻Hair DeathHair continues to
grow after deathHair highly
resistant to decomposition
Acids and bases have little effect
But bleaches will destroy hair and give you a bad hair day!
Hmm, I wonder what will happen if I just take one quick peek at my neighbor’s test in Foley’s class?
Hair as Evidence☻What hair can tell us about
a suspect☻Their hair characteristics
Color, length, width Spatial configuration
• Straight• Curly• Kinky
Cosmetic treatments (dyed, bleached, natural, damaged)
Signs of struggle (anagenic hair with parts of follicle)
Hair as Evidence☻Possible things learned
from hairSex (based on length)Age (greying of hair)Occupation (what is on the
hair, plaster,
sawdust, other chemicals)Drug use (1 inch hair gives
you 25 days
of drug use)
Hair as Evidence☻What hair can’t tell us
about a suspectHair cannot tell us who
someone is not individualizingException – DNA in root
☻ A fiber is the smallest unit of a textile material. Examples: Clothing Rugs Curtains
☻ Fibers can be Natural fibers
• Animal, vegetable, or mineral fibers Derived fibers
• Less used, cheaper plant materials turned into a more useful
• Technically man-made fibers like Rayon Synthetic fibers
• Chemically made fibers• as man-made fibers such as nylon
Natural Fibers: Animal fibers☻Wool
sheep hair spun into fibers and used in many textile products
Has all the characteristics of a hair (medulla, cuticle, etc)
☻Feltpressed rabbit or cow hairs produce a material
that is soft and pliableNatural felt has all the characteristics of a hair
(medulla, cuticle, etc)☻Silk
The thin fibers produced by silkwormsExtremely strong for its thickness
Natural Fibers: Plant or vegetable fibers☻Cotton
Seed head fibers (think dandelion) used in many textile products
Has flattened, twisted look to it☻Linen
A stem fiber used in table clothes and other textiles
Has a bamboo look to its fibers☻Hemp
A rougher stem fiberUsed in making natural rope
and other tough cloth items
Natural Fibers: Mineral fibers☻Asbestos
A fibrous material used for its heat insulating properties
Some forms highly carcinogenic (cancer causing)
Very spikey looking in photo
Derived Fibers☻Man-made fibers derived from natural materials
Classified as semi-syntheticFibers made from other substances normally
not used as fibersExample: cellulose in Rayon socksCellulose is
pulverizedThen extruded
like PlayDoh into fibers
Synthetic fibers☻Completely man-made, chemical fibers☻All are polymers
substances composed of chains of smaller individual units
Nylon• thermoplastic, silky material• First used in making parachutes and nylon
stocking in World War II• Strong, though original forms could tear • Ripstop nylon – will not tear completely
Dacron• PETE (Polyethylene terephthalate)• Also used in making beverage and other food
containers Polyester – another common synthetic fiberFiberglass – high insulating factor
How long do fibers persist?• Most fiber evidence is lost (fall off) a short
time after the transfer occurs. • The fibers that do remain will be persistent.• But most fibers, up to 80%, lost in first
24 hours
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