Trace Evidence Part I
Trace Evidence Review
A.Trace Evidence – refers to




Aka:
minute (tiny) physical evidence
that may be transferred
between a perpetrator to a victim
or to and from the crime scene
Locard’s Exchange Principle!
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!
C. Types of Trace Evidence
1) Hair - animal or human
2) Fibers - textile products (sheets, rugs,
clothing)
3) Soil - - the materials found in your garden!
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 notes
1) 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 – History
D. 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 terminology
Magnification
☻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
E. Microscope terminology
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 Microscope
1.
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)?
G. Types of Microscopes
Standard
Compound Light
Microscope
☻ typical
“biological”
scope
☻ used for


Hair, fibers
Blood and
tissue
☻ medium
magnification
(40x – 1,000x)
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
Aim TE 2 – How is hair used as
evidence in forensics?
Hair Function
 an appendage for maintaining warmth
 Found on various body parts
Hair 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
☻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
☻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 Death
 Hair continues to
grow after death
 Hair 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
hair
 Sex
• 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 suspect
Hair cannot tell us
who someone is
not individualizing
Exception – DNA in
root
Aim TE 3 – How are fibers used as
evidence in forensics?
☻ 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)
☻Felt
 pressed rabbit or cow hairs produce a material
that is soft and pliable
 Natural felt has all the characteristics of a hair
(medulla, cuticle, etc)
☻Silk
 The thin fibers produced by silkworms
 Extremely 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 fiber
 Used 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-synthetic
Fibers made from other substances normally
not used as fibers
Example: cellulose in Rayon socks
Cellulose is
pulverized
Then 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
Synthetic fibers
☻Completely man-made, chemical fibers
Dacron
• PETE (Polyethylene terephthalate)
• Also used in making beverage and other
food containers
Polyester
• another common synthetic fiber
• Often mixed with cotton to make more
comfortable, but increase strength of
cotton
Fiberglass
• Spun glass
• 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.
• 80% gone in 24 hours!