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