trace evidence

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Trace Evidence

Any small pieces of material, naturally

occurring or man-made.

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Hair as Evidence

Abundant (very common) Time will not change it Easily lost Mostly class evidence. Used most often for sexual assault

and violent assault

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Hair as Evidence Human hair is one of the most frequently found pieces

of evidence at the scene of a violent crime – 31. It can provide a link between the criminal and the crime. Hair is not living tissue. (14.)

From hair one can determine (29.): If the source is human or animal Race (sometimes) Origin of the location on the source’s body Whether the hair was forcibly removed If the hair has been treated with chemicals If drugs have been ingested

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Hair Morphology

The Study of Structure and Form

Parts of the hair Shaft--part of the hair

that sticks out of the skin

Root--lies below

the epidermis

Follicle—organ from

which the hair grows (source of DNA)

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Three Layers of the Hair Shaft

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Hair ShaftComposed of:

Cuticle—outside covering, made of overlapping scales

Cortex—inner layer made of keratin and imbedded with pigment; also contains air sacs called cortical fusi

Medulla—inside layer running down the center of the cortex

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Hair CuticleThe cuticle is the outermost layer of hair which is covered with scales. Scales always point toward the tip of the hair. These scales differ between species of animals and are named based on their appearance.

25. Usually scale impressions are made in fingernail polish or similar material then they are viewed under the microscope.

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Scale TypesMosaic Chevron

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Rabbit chevron scales

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Cat mosaic scales

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Pectinate Imbricate

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Human - Imbricate scales

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Scale TypesPetal Diamond Petal

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Dog – petal scales

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Hair CortexThe cortex is made up of spindle-shaped

cortical cells that are aligned parallel to the

length of the hair, giving the hair its shape.

It has two major characteristics: Melanin--pigment granules that give hair

its color Cortical fusi--air spaces, usually found

near the root but may be found throughout the hair shaft

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The medulla is the central canal running through the hair core that is not always present.

The medulla comes in different types and patterns.

Types: Continuous

Intermittent or interrupted

Fragmented

Absent--not present

Hair Medulla

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Hair Medulla Patterns

Uniserial

Multiserial

Vacuolated

Lattice

Amorphous (without a distinct pattern)

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Medullary IndexThe index measures the diameter

of the medulla relative to the diameter of the hair shaft.

Medullary Index for human hairis generally less than 1/3.

For animal hair, it is usually greater than 1/2.

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Human medulla - continuous

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Cat medulla

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Rabbit medulla

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Cow medulla

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Deer medulla (not scales!)

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Hair RootThe hair root is the end in the follicle from which

the hair grows.

The length of hair grows 0.5 mm per day or 1 centimeter per month.

There are three phases of hair growth:

Anagen--hair that is growing up to 6 years; root has a flame shaped appearance and may have a follicular tag from which DNA may be obtained.

Catagen--hair at rest for 2-3 weeks; has elongated appearance

Telogen--hair growth is ended; has club shaped appearance.

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Anagen

Forcibly removed hair shows damage and stretching of the root

Fallen out

Forcibly removed

Forcibly removed 13 &15. Follicular tag -Attached livingtissue (only sourceof DNA)

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Catagen

Dormant, resting root gets longer and

thinner.

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Telogen

Naturally shed hairs display club shaped root

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Human root

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Cat root

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Hair Identification Animal vs. Human

Cat Human

Scale Structure

Medullary index

Medullary shape

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Rabbit root

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Electron Microscope Picture of Sheep Hair

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Hair IdentificationComparison

Length

Diameter

Color intensity of pigments granules

Dyed hair has color in cuticle and cortex Bleaching removes pigment and gives

yellow tint

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Hair IdentificationOrigin of Human Hair

Head hair- shows little diameter variation and more uniform distribution of pigment color

Beard hair- coarse and have blunt tips due to being cut

Pubic hair- short and curly, with wide variation in shaft diameter, or buckling, and have a continuous medullae

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Tips of Hair

Blunt if recently cut Rounded if cut and allowed to grow Blackened or frayed show presenc

of a flame If broken end will be irregular

Broken Broken

Razor Cut Old Cut Burnt

New Scissor Cut

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Hair Shape

Can be straight, curly or kinky depending on the cross-section, which may be round, oval or crescent-shaped

Round(Straight)

Oval(Curly)

Crescent moon (Kinky)

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Determination of Race

Black/Africanhairs are kinky, containing dense, unevenly

distributed pigments, diameter is elliptical and varies in size

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Caucasian

hairs are straight or wavy, with very fine to coarse

pigments that are more evenly

distributed, oval diameter which varies in size

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Asian Hair Usually round constant diameter

Thick cuticle

Prominent medulla

Pigments are dense and often arranged in large patches

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Hair IdentificationDetermination

Age and Sex- only infant’s hair can be determined; sex cannot be determined

Individualization - DNA analysis could provide a link from questioned hair to standard hair (follicular tag actually the source not the hair itself)

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These 3 methods can be done at the crime scene or in the crime lab.

1. Visual Inspection Use naked eye or hand lens. Evidence removed and packaged for later

analysis Use bright light and forceps to collec

Collection of Trace Evidence

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Small paper envelopes are bad (Holes allow small objects to escape).

Use small plastic bags, glass vial or paper using a druggist fold.

Double package. Label each package.

Packaging from Visual Inspection

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Clear tape is used. Repeatedly apply tape to small area until most of

the stickiness is gone. Tape is folded back upon itself, taped to a glass

slide or taped to a piece of plastic. Put in separate labeled container.

Be sure to document specific area covered.

2. Tape Lift

36. Collection

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3. Vacuuming

Nozzle should be short and transparent.

Debris is collected on a filter or membraneSmall area is vacuumed. (Filters changed frequently)

Filters packaged in separate labeled container. (Be sure to document specific area covered)

Most improperly used method because it often results in the collection of a lot of irrelevant material.

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Collection of Hair Evidence Questioned hairs must be accompanied

by an adequate number of control samples. from victim possible suspects others who may have deposited hair at

the scene Control Sample

50 full-length hairs from all areas of scalp 24 full-length pubic hairs

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Hair Toxicology Advantages:

Easy to collect and store Is externally available Can provide information on the

individual’s history of drug use or of poisoning.

Collections must be taken from different locations on the body to get an accurate timeline.

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Hair Toxicology Napoleon died in exile in

1821. By analyzing his hair, some investigators suggest he was poisoned by the deliberate administration of arsenic; others suggest that it was vapors from the dyes in the wallpaper that did him in.

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Comparison Microscope

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Comparison Microscope

An optical bridge allows viewing of evidence side by side.

Useful for comparing bullets, fibers, hair…

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Fibers

Any small, elongated pieces of material used to manufacture cloth,

carpet, paper, cardboard, rope, cord, or string.

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Carpet Fiber and Dust

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Types of Fibers-Classification

Man-made Regenerated Synthetic

Natural Animal -

Protein Plants-

Vegetable Excrement Mineral

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TYPES NATURAL FIBERS

Animal or Proteinsheep (wool)goats (mohair, cashmere)camelsllamasalpacasvicunas

Fur fibers: mink, rabbit, beaver, and muskrat

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PolymersPolymers are basic chemical

substances of all synthetic fibers, long-chained molecules

Monomers-repeating molecular units of polymers

Importance- Synthesize many new items including glues, plastics, paints and fibers

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Collection of Fiber Evidence Bag clothing items individually in paper bags.

Make sure that different items are not placed on the same surface before being bagged.

Make tape lifts of exposed skin areas of bodies and any inanimate objects

Removed fibers should be folded into a small sheet of paper and stored in a paper bag