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Trace Evidence

Any evidence small in size, such as hairs, fibers, paint, explosives, glass, and soil samples, that would be analyzed utilizing microscopic techniques

Trace Evidence

Hair

&

Fibers

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Hair

• Hairs can be grouped by racial origin and body location

• Hair examiners can eliminate a suspect, but can not identify a suspect based on physical characteristics

• DNA testing can allow identification of a suspect

– Need root &/or attached skin for DNA sample

Fur

• Furs can be classified by species with a microscope

• Individualization is difficult

• Can determine color, length, and curliness

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Animal Hair Types • Guard hairs

– Outer coat

– Protection

• Fur/wool hairs

– Inner coat

– Insulation

• Tactile hairs

– Usually found on head (i.e. whiskers)

– Sensory function

• Tail/mane hair

Composition of Hairs and Furs

1. Keratins

2. Melanin

3. Trace Metals

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Keratins

• Sulfur-containing proteins that are interlocked to form stable fibrils

– Fibrils are very fine fibers

• Melanin

– Pigments

– Eumelanin (brown)

– Pheomelanin (red)

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• Trace Metals

– Deposited in the fiber during its growth stage from environmental contaminations

– What do you think about presence of drugs?!?

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Hair Structure • Shaft of the hair extends out of the skin

– Fibers composed of dead cornified cells

• Root embedded in the tissue

– Lower end expands to form the root bulb

– Growth takes place at the papilla

•Proximal End

Root portion

•Distal End Tip away from the root

Hair Structure

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• Cuticle – The outermost layer of hair

formed by overlapping scales

• Cortex – Main body of hair containing

protein fibrils, pigment, cortical fusi, and ovoid bodies • Coritcal fusi- microscopic air

pockets or vacuoles; usually near root of mature hair

• Ovoid bodies- oblong shaped concentrations of pigment

• Medulla – Lengthwise central canal of a

hair shaft

H a i r S t r u c t u r e

Cuticle

• Layer of scales covering the shaft

– Scales point away from proximal end & toward distal end

• Three types (many variations within)

– Coronal (crown-like) scales

– Spinous (petal-like) scales

– Imbricate (flattened) scales

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Coronal Scales

• Resemble stacks of paper cups

• Characteristic of very fine hairs

• Found on small rodents and bats, rarely humans

Spinous scales

• Triangular in shape

• Protrude from shaft

• Not found on humans

• Found on cats, seals, and near roots on minks, etc…

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Imbricate scales

• Overlap, like shingles of a roof

• Found on humans and other animals

Cortex • Characteristics important for human hair

identification

• Microscopic features: pigment, color, size, distribution, cortical fusi, ovoid bodies

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Cortical Fusi

Human

Human

Chest

Hair

Coyote

Dog

Ovoid Bodies

Human Dog

Cattle

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Pigment Granules- vary in color, size, distribution

Human Hair: granules

distributed toward cuticle

Red Human

Hair: granules

distributed

more toward

cortex

Animal Hair: granules

distributed toward medulla

Medulla • Humans: amorphous

& vacant of material

• Animals: contains cells arranged in species-specific manner

• Continuous, discontinuous, fragmentary, or not observable

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Medulla

• Structures regular/well defined in nonhumans

– Uniserial and multiserial ladders= rabbit hairs

– Lattices= deer hairs

– Vacuolated or cellular types (with varied shapes)= many animal species

Ladder

Uniserial Multiserial

Rabbit Hair

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Lattice (deer hair)

Stages of Growth

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Stages of Hair Growth Explained

Anagen Phase •Primary growth stage •When hair is growing

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Catagen Stage

•Dormancy stage •Transitional stage until hair is shed

Telogen Phase

•Final stage •Hair ready to shed

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Trace Evidence: HAIR

• Hair Evidence

– Laboratory analysis of:

• Animal or human hair

• Similar source: match, no match, inconclusive, known exemplars

• Body location

• Racial origin

• Color, length, degree of curl, diameter of shaft

• Cut, pulled, or shed

• DNA

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Animal or Human?!? Human

• Root – Club-shaped

• Color/pigmentation – Consistent throughout

shaft

– Evenly distributed or slightly dense towards cuticle

• Scales – Imbricate

• Medulla – Amorphous or not present

– Width < 1/3 diameter of shaft

Animal

• Root – Variable

• Color/pigmentation – Banding: radical color changes

– Distribution & density good identifiers

– Centrally distributed, more dense toward medulla

• Scales – Variable

• Medulla – Continuous & structured

– Occupies area > 1/3 diameter of shaft

Hair Evidence: Body Location

• Head

• Pubic area

• Limb

• Beard

• Chest

• Axillary

• other

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Hair Evidence: Age

• Not possible by microscopic examination

• Elderly hair

– Pigment loss

– Finer

– Variable diameter

Hair Evidence: Racial Origin • Head hairs show most distinguishing

characteristics

• Complicated to determine racial origin of infants and people with mixed racial profile

– Infants have very fine hair

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Hair Evidence: Racial Origin • Caucasoid

– Straight or wavy

– Round or oval cross-sections

– Evenly distributed medium-sized pigment granules

• Negroid

– Curly or coiled

– Oval cross-section

– Large pigment granules clumped in groups

– Hair shaft twists or buckles (commonly splits)

Hair Evidence: Racial Origin

• Mongoloid

– Straight

– Circular cross-section

– Medium-sized pigment granules grouped in patches

– Thicker cuticles

• Mixed origin

– Difficult to identify

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Hair Evidence: Color • Only 2 hair colors

– Red (pheomelanin) & Brown (eumelanin)

– Everything else is just a shade

• Random fact:

– Black hair is more common in men; blond and red hair more common in women

Hair Evidence: Color • Dyed

– Demarcation lines= distinct boundary between treated portion of hair and newly grown portion with natural pigment

• Multiple lines of demarcation

– Dye color in cuticle

– Evenly distributed hair color

– Hair color not a natural color

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Hair Evidence: Color • Bleaching

– Results from artificial bleaching process or from sun exposure

– Demarcation line between treated and natural hair growth

• Not as distinct in solar-bleached hair

• Multiple lines of demarcation

– No or few pigment granules in bleached portion

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Hair Evidence: Shed, Cut, Pulled

SHED

SHED

SHED

POSTMORTEM

Pulled:

notice

damage

to bulb

CUT

CUT w/ razor

Pulled:

notice attached

skin tissue

Hair Evidence: DNA • DNA taken from cells associated with root

• Determination of:

– Identity

– Sex

– Paternity

– Maternity (mitochondrial DNA)

• Roots of hair in anogen phase contain more DNA than ones in telogen phase

• More telogen hairs are available….why?

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Fibers

Fibers

• Most often used as class of evidence

• Can provide strong corroborating evidence to place perpetrator @ crime scene

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• Fiber

– Many filaments twisted or bonded together to form thread or yarn

• Filament

– Single strand of material of indefinite length

• Can be natural

– Silk, wool, mohair, cashmere, angora, cotton, linen, jute, sisal, hemp ,ramie ,asbestos, fiberglass, rayon

• Can be artificial or synthetic

– Acrylic, aramid, nylon, olefin, spandex, polyester ,modacrylic

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• Physical properties

– Color

• Chromatography of dyes

• Polarization with light

– Blend and/or weave

– Diameter of fibers

– Cross-sectional shape

• Physical properties

– # of filaments

– Density

– Refractive index

• Refraction is the bending of light waves due to change in the velocity

– Flourescence

• Flourescence is emission of light by a substance that has absorbed light or other electromagnetic radiation of different wavelengths

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• Chemical properties

– Burning tests (oxidation) analysis

• ash, behaviour in and out of flame, odor

– Thermal decomposition

• pH, residue and component chemicals

– Chemical decomposition

• Treatment with various strong acids, bases and solvents

• Many of these tests would be made between unknown and known

– Reference samples taken at scene

– Reference samples taken from individuals involved at scene

– Exemplars- scientific standards accepted widely

• Usually found in databases

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The End