Trace EvidencePart II

Summary

Microscopic Analysis Types of Trace Evidence

Glass Hair (fur) Fibers

Paint Soil Gunshot Residue

Hair

What is hair? What crimes are hair involved in? How is hair collected? How is hair analyzed in the lab?

What is hair?

Natural fibers of animal origin Terms: human = hair; animal = fur Usually growing (live root)

Trace > Hair

Cellular material in the hair shaft (mtDNA)

Good DNA in the hair root for forcibly removed hairs (STR)

Trace > Hair

What is hair?

What crimes are hairs involved in?

Hairs are shed from people; can link a person to a crime scene.

Animal fur may also link a person to a crime scene.

Trace > Hair

Visually by hand or with forceps. Possibly tape lift. Packaged in sealed containers.

Trace > Hair

How is hair collected?

Look at class characteristics (microscope):

Color Medulla, Cortex, Cuticle

Trace > Hair

How is hair analyzed?

Medulla: Species ID or human ID Present, absent, or fragmented

Line down middle of hair

Trace > Hair

How is hair analyzed?

Cortex: Color of hair Species ID or human ID May contain pigment blotches May contain air pockets

Trace > Hair

How is hair analyzed?

Cortex:

Humans = 1 color entire length Animals = color can vary at

root/middle/tip

Trace > Hair

How is hair analyzed?

Cuticle:

“Scales” on outside of hair Species ID only Humans = imbricate

Trace > Hair

How is hair analyzed?

How is hair analyzed? (cuticle)

Procedure: Put clear nail polish on slide. Place hair in nail polish; wait

to harden. Remove hair; look at

indentations in nail polish (microscope).

Trace > Hair

Fibers

Fibers are very useful as trace evidence:

Vary widely in class characteristics color, shape, chemical composition, etc.

Easily transferred from one source to another (carpets, clothes, etc.)

Significant persistence (won’t degrade)

How are fibers used as evidence?

As with other trace evidence, fibers can be transferred to/from a person or objects linking them to one another.

Trace > Fibers

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.

Trace > Fibers

Fibers can be classified into three main categories:

Natural (animal, plant, mineral) Manufactured Synthetic

Trace > Fibers

Natural Fibers:

Found in nature Can be artificially colored or treated

Cotton Wool Hemp

Trace > Fibers > Natural

Animal Fibers

Wool - Hairs from sheep Most common of animal fibers Hairs are spun to form thread

Silk - comes from silkworm Spun as double filament (separated before use)

Because of length, doesn’t shed easily

Other Hairs from Animals

Trace > Fibers > Natural

Plant Fibers

Cotton - seed hairs of cotton plantby far most common fiber (find almost everywhere)

Under microscope, fibers resemble twisted ribbon

Trace > Fibers > Natural

Linen - stem fiber from flax plant

Kapok - from seed hairs of kapok plant

Other fibers - Manila, hemp, sisal, jute

Other Plant Fibers:

Trace > Fibers > Natural

Mineral Fibers

Asbestos - crystalline material Used to be used for insulation Fractures into thin rods that

can get into your lungs; can kill you

Not used much anymore

Trace > Fibers > Natural

Filament: Long continuous fiber (like silk)

Staple: Filament is cut into smaller pieces; staples are spun together to form thread (like cotton)

Trace > Fibers

Filament vs. Staple

Manufactured Fibers

Regenerated Fibers

Trace > Fibers > Manufactured

Example: Rayon

Cellulose is dissolved, then resolidified to form the polymer fiber

Can occur in filament or staple form

Examples:

Nylon and Polyester

Man made Can also be filament

or staple

Trace > Fibers > Synthetic

Synthetic Fibers

Acrylics More common as

evidence Usually in staple form Staples spun together,

similar to wool

Trace > Fibers > Synthetic

Synthetic Fibers

Begin by identifying and comparing class characteristics for unknown sample (evidence) and known sample.

Unknown Known

Trace > Fibers > Analysis

Fibers from rug in a van.

Fibers found on victim.

Trace > Fibers > Analysis

Class characteristics

Trace > Fibers > Analysis

Color: microscopic examination

Size: length and width can be measured

Shape: cross section is viewed

Refractive Index – n. The ratio of the speed of light in air

or in a vacuum to the speed of light in another medium. Other microscopic properties (PLM)

Trace > Fibers > Analysis

Class characteristics

Chemical Composition: determined by advanced instrumentation

Trace > Fibers > Analysis

Class characteristics

Threads, Yarn, Rope, Cordage

Smallest component is fibers (staple) twisted together to form thread or is a filament.

This thread can then be twisted with other threads to form a thicker thread (string, etc.)

This thicker cord can then be twisted with other thicker cords, etc.

Trace > Fibers > Cordage

Threads, Yarn, Rope, Cordage

At each step, the number of cords can be counted.

At each step, the twist direction is either “S” or “Z”

Small cords or fibers twisted together to form larger cords

Trace > Fibers > Cordage

Fiber niso nll n Biref MP (ºC)

K1 1.518 to 1.528 1.544 to 1.551 1.505 to 1.516 0.035 to 0.039 Does not melt

K2 1.777 to 1.877 2.050 to 2.350 1.641 to 1.646 0.200 to 0.710 Does not melt

K3 1.512 to 1.521 1.510 to 1.520 1.512 to 1.525 -0.001 to -0.005

Does not melt

K4 1.538 to 1.539 1.530 to 1.539 1.538 to 1.539 -0.000 to -0.002

192 – 210

K5 1.533 to 1.545 1.568 to 1.583 1.515 to 1.526 0.049 to 0.061 210 – 230

K6 1.540 to 1.541 1.577 to 1.582 1.515 to 1.526 0.056 to 0.063 250 – 264

K7 1.522 1.553 1.507 0.046 182 – 186

K8 1.535 to 1.539 1.568 to 1.574 1.518 to 1.522 0.050 to 0.052 133 – 138

K9 1.567 to 1.575 1.632 to 1.642 1.534 to 1.542 0.098 to 0.102 282 – 290

K10 1.474 to 1.478 1.474 to 1.479 1.473 to 1.477 0.002 to 0.005 245 – 260

Q 1.520 1.515 1.513 -0.003 Does not melt

Glass

What is glass? What crimes are glass involved in? How is glass collected? How is glass analyzed in the lab?

What is glass?

Made from fused inorganic materials Amorphus; not crystalline (molecules not arranged)

Varies in elemental formula Many shapes and colors

Trace > Glass

How is glass involved in crime?

Small fragments can be used as trace evidence (link objects/people)

Crime scene reconstruction

Trace > Glass

How is glass collected?

For reconstruction, detailed photographs can be taken or the entire pane of glass is collected.

Trace > Glass

For trace evidence, usually visually collected with forceps and packaged in plastic bags.

Trace > Glass

How is glass collected?

For reconstruction:

Radial cracks

Concentric cracks

Trace > Glass

Radial cracks

Concentric cracks

Concentric cracks

Trace > Glass

For reconstruction:

When looking at a radial section, conchoidal fractures point back to the origin of the break

Core usually on opposite side of the origin

Trace > Glass

For reconstruction:

1. Determine the direction of projectile.

1

2

3

Trace > Glass

For reconstruction:

2. Determine the order of projectiles when dealing with more than one.

1

2

3

Trace > Glass

For reconstruction:

2. Determine the order of projectiles when dealing with more than one.

For trace analysis:

Done with microscopic analysis Color, curve, thickness, etc. Refractive index: Determined by placing glass

in oils of different refractive indexes

Trace > Glass

Associate unknown glass found at the crime scene with known samples to determine the source.

Refractive index:

Low relief = no outside line R.I. of glass and oil are similar

High relief = thick outside line (Becke line) R.I. of glass and oil are different

Trace > Glass

Paint

What is paint? What crimes are paint involved in? How is paint collected? How is paint analyzed in the lab?

What is paint?

Colored chemical coating Covers cars and houses

Trace > Paint

Paint contains 3 things: Vehicle – binds components together Pigment – gives paint color Extenders – used to modify gloss, texture,

opacity, etc.

What is paint?

Trace > Paint

What crimes are paint involved in?

Hit and Runs – paint from car left at scene Other vehicular accidents Home invasion – windows; on suspect

Trace > Paint

How is paint collected?

Visually by hand or with forceps. Packaged in sealed containers.

Trace > Paint

How is paint analyzed?

1. Possibly a physical match (jigsaw-like)

2. Associate the unknown paint with a known sample (class characteristics)

Trace > Paint

Chemical composition determined by FT-IR

Trace > Paint > Analysis

How is paint analyzed?

Chemical “Fingerprint”

Paint can be in multiple layers

Each layer is analyzed to determine its physical and chemical properties.

Trace > Paint > Analysis

Soil

What is soil? What crimes involve soil? How is soil collected? How is soil analyzed in the lab?

What is soil?

Mixture of animal and vegetable materials, and minerals

In many ways, soil has a unique composition in a given area.

Trace > Soil

What crimes involve soil?

Due to the widespread location of soil (earth), it can be used to associate people, objects, and scenes in numerous cases.

Trace > Soil

How is soil collected & analyzed?

Materials in soil are identified and quantified.

Analysis relies on soil composition being: Consistent over time in one location Different in different locations

Trace > Soil

Collected in jars or vials.

Gun Shot Residue (GSR)

What is gun shot residue (GSR)? What crimes are GSR involved in? How is GSR collected? How is GSR analyzed in the lab?

What is GSR?

Mixture of materials that originate from the firing of a gun.

From the chamberFrom the

barrel

Trace > Gun Shot Residue

GSR will fall onto hands of person firing the gun.

Trace > Gun Shot Residue

What is GSR?

What crime is GSR involved in?

Crimes with guns

Trace > Gun Shot Residue

How is GSR collected & analyzed?

Hand/glove/paw is swabbed

Trace > Gun Shot Residue

Elements barium and antimony are found in high levels.

Use powerful microscopy (SEM) Use chemical tests (color change reactions)

Analysis: