Trace Evidence Part I

Trace Evidence Part I

Trace Evidence Review • 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 Aka: 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!

Types of Trace Evidence • Hair - animal or human • Fibers - textile products (sheets, rugs, clothing) • Soil - - the materials found in your garden! • Botanicals - assorted plant parts including pollen • Glass – assorted sources • Paint – car in particular • Other – bits and fragments of materials

The Microscope – History • Historical notes • 1590’s - Zacharias Janssen • Dutch • Built first simple microscope • Actually jailed at one point for counterfeiting • 1670’s - Anton Van Leeuwenhoek • Dutch • Father of Microbiology • improved the construction of the simple microscope • magnification increased to 270x !!!

The Microscope – History • Historical notes • 1660’s - Robert Hooke • English • built first compound light microscope • Drew huge numbers of organisms using it! • 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 • What is the width of the hair if the hair covers 1/5 of the FOV (FOV = 800 u)? • What is the size of a hair if the hair covers 1/6 of the FOV (FOV = 240 u)? • 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 • 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) • 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 • 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

Dog Mouse Cat • 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

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

Hmm, I wonder what will happen if I just take one quick peek at my neighbor’s test in Foley’s class? 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!

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!

Trace Evidence Part I