Forensic Test 4

What are the three basic components of paint?

• Solvent: Keeps the ingredients dissolved and makes paint easy to spread or spray.

• Binder: Holds the pigment to the surface after the solvent evaporates. Usually a polymer.

• Pigment: Gives paint its color.

What is the purpose of a solvent?

It keeps the other ingredients dissolved and makes the paint easy to apply.

What is the purpose of a binder?

It binds the pigment to the painted surface after the solvent evaporates.

What is the purpose of a pigment?

It provides the paint's color.

Why can forensic analysts distinguish paints made by different manufacturers?

Manufacturers use different formulations of binders and pigments, creating distinguishable chemical and physical characteristics.

What are the four basic layers of an automobile paint job, from innermost to outermost?

1. E-coat (electrocoat)

2. Primer

3. Basecoat (colorcoat)

4. Clearcoat

Do factory automobile paint jobs have individual or class characteristics?

Generally, class characteristics, because many vehicles are painted using the same manufacturing process.

How can repainting affect forensic paint analysis?

Additional layers may create unusual combinations of colors and materials that can provide more distinguishing characteristics.

hat are the other important characteristics of a paint chip?

Topcoat color and surface texture, along with other physical and chemical properties.

How do forensic analysts examine paint-layer sequences?

They examine the edge or cross-section of a paint chip using a stereoscopic microscopeor comparisonmicroscope.

What is infrared microspectrophotometry (IRMS)?

A technique that combines microscopic examination with infrared spectroscopy to analyze the chemical composition of very small samples.

How does IRMS work when analyzing a paint chip?

1. The analyst views the paint chip's cross-section under a microscope.

2. The analyst selects a particular layer.

3. Infrared light is directed at that layer.

4. The instrument measures infrared absorption and produces a spectrum.

5. The spectrum helps identify the binder's chemical composition.

6. The process can be repeated for other layers.

Why is the microscope important when using IRMS?

It allows the analyst to target a very small area or individual layer instead of analyzingthe entire paint chip atonce.

What does an infrared spectrum reveal?

Information about molecular vibrations and chemical bonds that helps identify thesubstances present.

What is pyrolysis gas chromatography?

A technique used to analyze the chemical composition of a material by heating it in the absence of oxygen, then separating and identifying the resulting volatile products using gas chromatography.

How is pyrolysis gas chromatography used in paint analysis?

• 
  A small paint sample is heated without oxygen.

• The paint decomposes and vaporizes into smaller compounds.

• The vapor is introduced into a gas chromatograph.

• The instrument separates the components for analysis.

• The results help characterize and compare paint binders.

What does PDQ stand for?

Paint Data Query.

Who created the PDQ database?

Royal Canadian Mounted Police (RCMP).

What information is stored in the PDQ database?

Information submitted by automobile manufacturers, including:

• Paint-layer colors and sequences

• Primer colors

• Binder composition

• Information that can help associate paint with vehicle makes, models, colors, and production years

who was known as “The Fox” in the case mentioned in your notes?

Malcolm Fairley, also known as “The Fox,” circa 1984.

What is the key forensic concept illustrated by a paint-evidence case?

Paint can connect evidence to a possible source through layer-by-layer comparisons and chemical analysis.

What detail about how paint evidence helped catch The Fox should you review?

Your supplied notes introduce the case but do not include the actual account of the investigation. Review the continuation of your class material for the specific evidence and how it led investigators to Fairley.

When a stain that looks like blood is found at a crime scene, investigators ask:

1. Is it blood?

2. Is it human blood?

3. If not human, what species is it?

4. If human, what is its blood type?

5. Whose blood is it?

Blood has two main components:

• Plasma: Liquid part of blood, mostly water. Contains antibodies.

• Solids: Includes red blood cells.

• Red blood cells (RBCs):

• Contain hemoglobin and antigens.

• Hemoglobin:

• Carries oxygen to cells and carbon dioxide to the lungs.

• Antigens:

• Found on the surface of red blood cells. Determine blood type.

• Antibodies:

• Y-shaped proteins found in plasma that attach to specific antigens.

Kastle-Meyer Test

• Uses phenolphthalein.

• Changes from colorless to bright pink.

Hemastix Test

• Uses benzidine (according to the notes).

• Changes from colorless to green.

Luminol Test

• Uses luminol.

• Produces a blue glow.

• Helps detect traces of blood that may not be visible.

Bluestar

• is a commercial product that works like luminol.

• Glows bright when blood is present.

• More stable than regular luminol.

• Bluestar and luminol are the most sensitive blood detection tests.

• Can detect very small amounts of blood.

False Positives

A false positive happens when a substance other than blood causes a positive result on a blood detection test.

substances that cause false positives:

• leach

• Horseradish

• Potatoes

Microcrystalline Tests

• Used to help identify blood.

• Reagent + blood = Crystals.

• Crystals have a specific size and shape.

• A microscope is used to examine the crystals.

• Less convenient to perform than color tests.

• Avoid many false positives associated with color tests.

The Four Blood Types

• Type A = A antigen, B antibodies.

• Type B = B antigen, A antibodies.

• Type AB = Both antigens, no antibodies.

• Type O = No antigens, both antibodies.

Agglutination

• When red blood cells clump together.

• Clumping happens when an antigen meets its matching antibody.

How to Determine Blood Type

1. Add A-type antibodies to a blood sample.

2. Add B-type antibodies to a fresh blood sample.

3. Observe whether the blood cells clump.

Understanding the Rh Factor

• D antigen present = Positive (+)

• D antigen absent = Negative (-)

direction of travel

which direction blood was moving when it hit a surface

angle of impact

the angle at which blood struck a surface

area of convergence

the approximate 2-dimensional location from which blood originated

position of individuals

possible locations of victims or suspects

low velocity

large drops

medium velocity

medium sized drops

high velocity

tiny drops or fine miss

gunshot spatter

consists of very tiny droplets

often appear as a fine mist

associated with high velocity impact

cast off

blood released from a moving blood covered object, such as a weapon

often appears as lines or arcs of blood droplets

arterial spurt pattern

occurs when a major artery is severed while the heart is still pumping

blood is projected in pulses

often creates an arcing pattern

void patterns

occurs when an object or person blocks blood from reaching a surface

leave an unstained area surrounded by bloodstains

can indicate where an object or person was positioned

contact/transfer patterns

occurs when a bloody object touches another surface

can create handprints, shoe prints or smears

can indicate contact between two surfaces

skeletonization

occurs as a blood drop begins to dry

blood dries from the outside toward the inside

a hardened outer skin forms

if something smears the drop before it completely dries a darker ring may remain

spatter

blood droplets distributed through the air

stringing

using strings to reconstruct blood flight paths

The word polymer is derived from two different terms: poly and mer. 

many, unit.

Which of the following terms is used to describe the individual units that make up DNA?

nucleotide

Which of the following make up the backbone of a DNA strand?

• Deoxyribose sugar

• Phosphate

Which of the following is a unique attribute of DNA between different people?

The sequential order of four bases along DNA.