TRACE EVIDENCE

Hair, Fiber, Soil and Glass Analysis

What is “Trace Evidence?”

Definition:some minute trace of a suspect’s presence

Ex. Hair, carpet fiber, clothing, seeds• Corresponds to Dr. Edmond Lockard’s

Principle“when a criminal comes in contact with an object or person, a cross-transfer of evidence occurs”

Examples of Trace Evidence

Dirt False Nails

Glass Earrings

Hair

Carpet

Clothing

Seeds

Leaves

Etc.

Recall: exemplars must be taken for comparison

- samples taken from known locations to be used as comparisons for unknowns

Hazardous Evidence1. Chemical threat- chemical accidentally

ingested through breathing (nose/mouth) or indirectly to mouth through touch (wipe of lips, etc.)

2. Biohazards- blood and body fluids can contain HIV, HEP, or other viruses; trace evidence that comes in contact with these is marked “Biohazard”

3. Explosive threat- gunpowder and explosives that are undetonated are hazardous to investigators

Trace Evidence - Hair

• Hair can be treated as any other fiber• Ethnicity can sometimes be determined but a

multicultural society is making it more difficult

Ex. 1/4 Mexican 1/2 Polish 1/4 Hungarian

• Drugs a person has used can be found in hair as well as DNA if scalp tissue present

• Easy to tell if a hair fell out or plucked; note angle of root to the rest of the hair shaft

Anatomy of Hair

Hair is made of KERATIN: protein-based materials in nails and horns also

Trace Evidence - Hair

Parts of Hair- Medulla runs the

center of the hair- Cuticle is outer

covering and can appear like pine cone scallops

- Cortex in the intermediary part

Types of Medullas in Hair

Facts About Hair

• Hair grows in three phases: anagen (actively growing), catagen (cell production reduced and bulb formed), telogen (no cell growth; easily falls out)

• Melanin gives hair color• Lose about 100 scalp

hairs a day

• If the root is stretched and follicle tissue attached, hair probably forcibly removed

Microanatomy

• Cuticle of a hair is a series of overlapping scales

• Human scale pattern: imbricate

(although other animals have as well)

Imbricate Scale Pattern

Humans

Microanatomy

• The cortex makes up the bulk of the hair

• Can contain ovoid bodies

• Also possible are cortical or medullary disruptions

Comparison of Hair3 Basic conclusions:a) Q hair exhibits same microscopic charac. as

K hair, then possible to have come from same person

b) Q hair exhibits similarities but slight differences to K hair, no conclusion can be made

c) Q hair exhibits different microscopic characteristics to K hair, concluded that hair did not come from the known source

Hair comparisons are NOT a form of positive identification!

Trace Evidence - Hair• Hair samples for examination (especially

rape cases) can consist of 100 or more and should be taken from the head and pubic regions

• May require use of a variety of light sources to find since hard to see w/ naked eye

• Animal hair medulla usually are thicker than humans

hair cell from inside an ear

Animal Hair vs. Human Hair

Animal Hair classified three ways:

1. Guard hairs that form the outer coat of an animal and provide protection

2. Fur or wool hairs that form the inner coat of an animal and provide insulation

3. Vibrissa or Tactile hairs (whiskers) that are found on the head of animals provide sensory functions

Trace Evidence Facts

• “Match” evidence - similar to exemplars, it is evidence that is collected to see if materials from one area match another

Ex. Duct tape used to wrap a body found in the woods “matched” to duct tape found at parent’s home

• Glass fragments can indicate where the glass came from, what direction it was shattered, what hit the glass, velocity speeds

Trace Evidence - Fibers

• Tape is not used to lift fibers because the residue contaminates fiber

• Samples of typical fibers of the victim are submitted as exemplars and are used to identify possible suspect fibers

• Fiber color, natural/synthetic, shape, and length examined under microscope

• Fibers are also tested chemically for topical sprays, fluids, drugs, etc.

What is a “fiber”?

• Either a natural or manufactured unit of matter that forms the basic structure of a fabric

• Length at least 100x its diameter

• Protein (AA); Cellulosic (Carbs); Mineral (Silica-Rocks/Sand); Synthetic (Polymers w/water and air)

Textile Fibers

• Filaments: indefinite or extreme length I.e. silk or manufactured fiber

• Staple fiber: natural (except silk) or cut filament usually 7/8 to 8 inches

• See pg. 392 in text for chart of Fiber Types

Yarn Twists

• Yarns are often formed from a number of smaller single yarns twisted together

• The twist patterns are Z, S, or no twist

Fabric Construction• Woven fabrics - 2

sets of yarn; interlaced

• Knit fabrics - interlocking loops of one or more yarns

• Non-woven fabrics - mechanically interlocked, random web/mat; bonded w/cement

Fiber Characteristics

• Crimp - waviness• Color - dye/pigments• Cross-sectional

shape - shape of filament when cut at right angle

Trace Evidence - FibersFibers/Cords/Ropes

examined by:

• Color (Huge Identifier)• Diameter of cross

section• Presence of staple or

filament fibers• Twist/braid/nontwist• Type of twist• Crowns or turns per

inch

• # of plies or braids• Twist of each ply or

braid• Filaments in each ply or

braid color• coatings

Color Assessment

• Metameric colors: colors that appear to match in one set of lighting but not in another

• Microspectrophometer: instrument that allows color measurement of individual fibers

Trace Evidence - Metal and Paint• Metal shavings

- result of tools- rare metal shavings can indicate what tool was used, even the manufacturer

• Paint- paint rubs/marks on one surface can be matched to items that rubbed it- paint from cars can be matched back to manufacturer- do not pick up paint chips with tape! It ruins the testing process; use tweezers or a brush and put into an envelope

Soil and Glass

• Often very underrated as evidence• Soil: earth material, either natural or

manmade that is transferred from a crime scene to a person or object or may have been shed and found at a different location

• Soil contains organic (living: humus, insects, plants) and inorganic (nonliving: minerals, rocks, trash) material

Soil and Glass continued…

• Time elapsed is important; soil comp could have changed

• Dry soil: plastic bag storage; Wet soil: paper or cloth to dry first

Trace Examiner’s Field Kit

• Evidence vacuum• Extra batteries• Filters• Photo equipment• Glass slides & coverslips• Tweezers/chopsticks• Light sources• Measuring tools

• Bindle (non-reactive) paper

• Lifters, acetate covers• Lifting tape, household

tape• Envelopes, boxes,

bottles• Cutting tools (saw,

knives, scissors)