FIS 201 Set 4 Exam 3 - Trace Evidence

What is trace evidence?

Small natural or artificial particles and fragments found at a crime scene.

What is transfer and divisible matter?

When something breaks, separates, or transfers partially, it retains properties of the original item and the process that separated it.

What are class characteristics?

Features shared by similar items or products that can narrow down the possible source.

What are individual characteristics?

Features unique to a particular item or transfer process that can help identify a specific source.

What are examples of artificial trace evidence?

Textile fibers, paint, glass, polymers, plastics, cosmetics, and adhesives.

What are examples of natural trace evidence?

Hair, pollen, soil, fire debris, diatoms, and metal fragments.

Why is trace evidence important?

It can connect people, objects, and locations through the transfer of small materials.

What are three methods of detecting trace evidence?

Visual examination, alternate light source (ALS), and collection methods.

What is an alternate light source (ALS)?

A light source used to help detect evidence that may be difficult to see under normal lighting.

What is a tape lift?

A collection method that uses adhesive tape to pick up very small particles or fibers.

When is a tape lift useful?

When evidence is too small or delicate to collect easily by other methods.

What are forceps used for in trace evidence collection?

They are used to manually pick up individual pieces of evidence.

What is a disadvantage of using forceps?

Collecting many tiny particles manually can be time-consuming.

How is a vacuum used to collect trace evidence?

A vacuum collects small particles on a filter for later examination.

When might a wet swab be used to collect trace evidence?

When collecting sticky substances such as glue.

How should loose hairs be preserved?

Place them in paper packaging.

How should tape lifts be preserved?

Press them onto clear plastic for storage.

How should loose trace materials be preserved?

Place them in suitable containers, such as cups.

How should glass shards be preserved?

Package them in cardboard containers.

What is a hair exemplar?

A known hair sample collected for comparison with questioned hair evidence.

How many head hairs are collected for a standard hair exemplar?

25 head hairs.

How many pubic hairs are collected for a standard hair exemplar?

25 pubic hairs.

What is cuticle casting?

A technique using acrylic to make a cast of the hair's cuticle pattern.

What is slide mounting?

Placing a specimen on a microscope slide for examination.

What is the medulla of a hair?

The innermost part of the hair shaft.

What is the human hair medulla generally like?

It tends to have a relatively simple structure.

What is the cuticle of a hair?

The outermost layer of the hair shaft.

What is the imbricate cuticle pattern?

A pattern of flattened, overlapping scales.

Can hair alone reliably identify a person's race?

Hair characteristics may provide limited information, but they cannot reliably establish a person's race.

Can hair comparison identify a specific person by itself?

Usually not. Hair comparison can provide class-level information, but DNA testing may provide stronger identification evidence.

What can an intact follicular tag provide?

Nuclear DNA that can be analyzed using STR testing.

What does STR stand for?

Short tandem repeat.

What type of DNA may be tested when a hair lacks a follicular tag?

Mitochondrial DNA (mtDNA).

What is anagen hair?

Hair in the active growth phase.

Why can an anagen hair be important in a forensic investigation?

It may have tissue attached, potentially providing nuclear DNA, and its removal may be associated with force.

What is telogen hair?

Hair in the resting phase that is eventually shed naturally.

Approximately how many hairs does a person lose per day?

About 100 hairs per day.

What instrument is used to compare hair samples?

A comparison microscope.

What are class-level characteristics of hair?

Shaft width, medulla thickness, and medulla shape.

What is fiber evidence?

Small strands of material that may transfer between people, objects, and locations.

Why are fibers useful in forensic investigations?

They vary widely, transfer easily, and may go unnoticed.

What is a fiber exemplar?

A known sample of fiber collected for comparison with questioned fiber evidence.

How should fiber exemplars be collected?

Collect representative fibers of each type and color.

What is a light microscope used for in fiber analysis?

Examining fiber shape and other visible characteristics, typically at magnifications up to about 400x.

What is a polarizing light microscope used for?

Examining properties such as refractive index, anisotropy, isotropy, and birefringence.

What is a scanning electron microscope (SEM)?

A microscope that uses electrons to produce highly magnified images, potentially up to about 500,000x depending on the instrument.

What is fiber morphology?

The visible shape, structure, and physical appearance of a fiber.

What is the first step in fiber analysis?

Examine the fiber's morphology using a light microscope.

How can the cross section of a fiber be examined?

Using a light microscope or scanning electron microscope.

How is the color of a fiber analyzed?

Using spectrophotometry.

How can the basic chemistry of a fiber be identified?

Using a polarized light microscope or spectrophotometry.

How can the specific chemistry of a fiber be identified?

Using chromatography and/or mass spectrometry.

What is natural wool fiber made from?

Animal hair.

What animals can produce wool fibers?

Sheep, goats, llamas, alpacas, and rabbits.

What cuticle pattern is associated with wool fibers?

Imbricate scales.

What is cotton fiber made from?

Plant cellulose.

What does cotton typically look like under a microscope?

A flat, twisted, ribbon-like tube.

What is silk fiber made from?

Material secreted by insects, especially silkworms.

What does silk typically look like under a microscope?

Smooth, with an elliptical to triangular cross section and variable thickness.

Why are fibers valuable as trace evidence?

They are easily transferred, come in many varieties, and may connect a person or object to a location.

What does the human eye detect when seeing an object's color?

Light reflected from the object.

What determines the color we perceive?

The wavelengths of light reflected by an object.

What is a spectrophotometer?

An instrument that measures the amount of light reflected or transmitted at specific wavelengths.

What can visible-light spectrophotometry tell investigators about a fiber?

Information about the color of its dye.

Why examine wavelengths beyond visible light?

Materials can interact differently with nonvisible wavelengths, revealing additional chemical information.

What is infrared (IR) spectroscopy?

A technique that uses infrared light to help identify a material's chemical composition.

Is infrared spectroscopy destructive?

It is generally nondestructive.

What can infrared spectroscopy identify?

Basic chemical families and information about a material's chemical composition.

How are unknown IR spectra identified?

By comparing their peaks with spectra in a library of known materials.

What should be compared when examining IR spectra?

The positions and patterns of the peaks.

What is paint?

A coating applied to an exposed surface.

What are the main components of paint?

Pigment, binder or modifier, and solvent.

What is the pigment in paint?

The component that provides color.

What is the binder in paint?

The component that holds the pigment together and helps the paint adhere to a surface.

What is the solvent in paint?

The component that helps the paint flow or spread and may evaporate as it dries.

When is paint commonly transferred as forensic evidence?

During vehicle accidents and collisions.

What is a paint chip?

A three-dimensional piece of paint that may preserve multiple paint layers.

Why are paint chips useful in forensic analysis?

They preserve the layers of paint, making comparison easier.

What is a paint smear?

Paint that has been briefly melted or smeared as two objects slide against each other.

What is a paint droplet?

A small amount of aerosolized paint that lands on a surface, such as clothing.

What is a paint exemplar?

A known paint sample collected for comparison with questioned paint evidence.

How is a full-depth paint exemplar collected?

By scraping through all paint layers from a vehicle or wall.

What are other sources of known paint samples?

Commercial samples and manufacturer samples.

What is a physical match in paint analysis?

Determining whether paint fragments fit together physically.

What is an important rule when attempting a physical match?

Do not force the pieces together.

What is layer comparison in paint analysis?

Comparing the number, thickness, order, and colors of paint layers.

What instrument can compare paint layers?

A comparison microscope.

How can paint color be analyzed?

Using a spectrophotometer or colorimeter.

What is a colorimeter used for?

Measuring color.

What can a spectrophotometer provide in paint analysis?

Information about color and the material's optical properties, which may help with chemical comparison.

Why should all visible paint components be examined?

Different layers or components may provide useful identifying information.

What is the Paint Data Query database used for?

Comparing automotive paint information by manufacturer, year, make, model, and paint code.

What is pyrolysis chromatography used for in paint analysis?

Analyzing paint components by heating them to break down material and separating the resulting compounds.

What is observed during pyrolysis chromatography?

The time at which peaks emerge from the analysis.

What is glass primarily made of?

Silicon dioxide (SiO2).

What type of solid is glass?

An amorphous solid, meaning its atoms do not have the regular repeating arrangement found in crystalline solids.

Why are other elements added to glass?

To change properties such as color and strength.

What properties of glass can vary?

Thickness, density, and refractive index.

What is laminated glass?

Glass made of two or more layers held together by a strong middle layer.

Where is laminated glass commonly used?

Windshields and bullet-resistant glass.