cte forensics/law & public safety 1-2

CTE Forensics/Law & Public Safety

1-2

Unit 4

Trace Evidence II:Paint, Glass,

& Soil

© 2013 by Pearson Higher Education, IncUpper Saddle River, New Jersey 07458 • All Rights Reserved

Learning Standards and Objectives

CTE: 6.0 = Analyze Investigative Procedures (6.1 - 6.7); Science: Strand 1 - Concept 1 PO 1 - 4; Concept 2 PO 1 - 5; Concept 4 PO 1 - 4; Strand 2 - Concept 1 PO 1 - 4; Strand 3 - Concept 2 PO 2; Strand 4 - Concept 1 PO 1 - 5, Concept 2 PO 1 – 4; Strand 5 - Concept 1 PO 1,2, & 4; Strand 6 - Concept 3 PO 9.

Students will be able To:

evaluate the use of the microscope for trace evidence and hair/fibers. To distinguish the history, characteristics, physiology, patterns, types, development & preservation; Continue to evaluate trace evidence (glass, paint, soil) using a comparison microscope; practicum exercise.

Measurements: : Quizzes, class discussions, comprehension assessments, performance assessments (labs).

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Key Terms – Be prepared for a Quiz

Pigments

Primer

Soda lime

Druggist fold or evidence fold

Float glass

Tempered glass

Laminated glass

Bullet proof glass

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Paint• Paint spread onto a surface will dry into a hard film

that can best be described as consisting of pigments and additives suspended in the binder.

• One of the most common types of paint examined in the crime laboratory involves finishes emanating from automobiles.

• Automobile manufacturers normally apply a variety of coatings to the body of an automobile.

• These coatings may include electrocoat primer, primer surfacer, basecoat, and clearcoat.


Methods for Paint Comparison• The wide diversity of automotive paint contributes to the forensic

significance of an automobile paint comparison.

• Questioned and known specimens are best compared side by side under a stereoscopic microscope for color, surface texture, and color layer sequence.

• However, paints can only be individualized if they have a sufficiently complex

layer structure.

• Pyrolysis gas chromatography and infrared spectrophotometry are invaluable techniques for distinguishing most paint binder formulations, adding further significance to a forensic paint comparison.

• Solid materials, such as paint, may be heated or pryolyzed to high temperatures so that they will decompose into numerous gaseous products to flow through the GC column.

• Crime laboratories are often asked to identify the make and model of a car from a small amount of paint and will make use of color charts for automobile finishes or the PDQ database.


Collection and Preservation

• Paint chips are most likely found on or near persons or objects involved in hit-and-run incidents.

• Paper druggist folds and glass or plastic vials make excellent containers for paint.

• Paint smeared or embedded in garments or objects require the whole item to be packaged and sent to the laboratory.

• Tools used to gain entry into buildings or safes often contain traces of paint, requiring the tool be collected, along with reference paint samples (control samples)

KEY POINT TO KNOW!• Uncontaminated standard/reference paint must always

be collected.


Glass Composition

•Glass is a hard, brittle substance that is composed of silicon oxides (sand) mixed with various metal oxides. • Sodium carbonate (soda) is normally added to the

sand to lower its melting point. • Calcium carbonate (lime) is also added to the sand

mix to prevent the glass from dissolving in water.

•Forensic analysts usually examine “soda-lime” used to manufacture most window and bottle glass.

http://youtu.be/Z-3XI5gSQok


Glass Composition• When molten glass is cooled on a bath of molten tin, this

is called float glass. http://youtu.be/_gQa_VGA0I4• Tempered glass is stronger than normal glass due to

rapid heating and cooling of the glass surfaces. http://youtu.be/f6oNmIDBmEo http://youtu.be/25aTEa0Of7Q

• Laminated glass found in car windshields has a layer of plastic between two pieces of ordinary window glass. http://youtu.be/qbIZjJ-7yYQ

• Security Glass (add to your notes http://youtu.be/x_CiLZY-HGw


The Making of Glass

Glass is a hard, brittle substance (add: amorphous solid (non-crystalline)

composed of 4 ingredients

1. sand

2. Silicon

3. Soda

4. Lime Glass Mtn. Selenite Crystals

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Forensic Glass Comparison

• For the forensic scientist, the problem of glass comparison depends on the need to find and measure those properties that will associate one glass fragment with another while minimizing or eliminating other sources.

• To compare glass fragments, a forensic scientist evaluates two important physical properties: density and refractive index.

• The FBI has created databases to correlate refractive index and density values of glass to their frequency of occurrence in the glass population of the United States.


Glass Flotation Method

• Density is defined as mass per unit volume.

• The flotation method is a rather precise and rapid method for comparing glass densities.

• In the flotation method, a glass particle is immersed in a liquid.

• The density of the liquid is carefully adjusted by the addition of small amounts of an appropriate liquid until the glass chip remains suspended in the liquid medium.

• At this point, the glass will have the same density as the liquid medium and can be compared to other relevant pieces of glass which will remain suspended, sink, or float.


Glass Immersion Method

The immersion method is best used to determine a glass fragment’s refractive index. The bending of a light wave occurs because of a change in its speed is called refraction.

• The ratio of the velocity of light in a vacuum to its speed in any medium determines the refractive index of that medium.

• This method involves immersing a glass particle in a liquid medium whose refractive index is varied until it is equal to that of the glass particle.

• The Becke line is a bright halo near the border of a particle that is immersed in a liquid of a different refractive index.

• At this point, known as the match point, the Becke line disappears and minimum contrast between liquid and particle is observed.


Analyzing Cracks in Glass

• The penetration of window glass by a projectile, whether it is a bullet or a stone, produces cracks which radiate outward (radial fractures) /and encircle the hole (concentric fractures).

• By analyzing the radial and concentric fracture patterns in glass, the forensic scientist can determine the direction of impact.

Comprehension Assessment: Describe the difference of radial and concentric fractures in glass and draw a picture on your note page.

http://youtu.be/dwnBGnKSG2o


Analyzing Cracks in Glass

• A high-velocity projectile, such as a bullet, often leaves a hole that is wider at the exit side; hence its examination is important in determining the direction of impact.

• The direction of impact can also be accomplished by applying the 3R Rule: Radial cracks form a Right angle on the Reverse side of the force.

(multiple)• The sequence of impacts when there have been

successive penetrations of glass is frequently possible to determine because a fracture always terminates at an existing line of fracture. Uh? Can you explain that?


Which eamples are centrical and radial fractures.


Collection of Glass

• If glass fragments can be pieced together, every effort must be made to collect ALL the glass found.

• Even if the glass is so small it can’t be pieced together, it still must be collected to examine for traces of hair, blood, bodily fluids , prints and connections.

• The evidence collector must submit all glass evidence found in the possession of the suspect (on clothes or in cuts), along with similar/connected samples of broken glass at the crime scene.

• The glass fragments should be packaged in solid containers or in brown paper placed in another padded envelope, to avoid further breakage.

• If the suspect’s shoes and/or clothing are to be examined for the presence of glass fragments, they should be individually wrapped in paper and transmitted to the laboratory.


Soil• The value of soil as evidence rests with its

prevalence at crime scenes and its transferability between the scene and the criminal.

http://youtu.be/PvxJ_HhXSiQ

• Most soils can be differentiated by their gross (basic) appearance.

• A side-by-side visual comparison of the color and texture of soil specimens is easy to perform and provides a sensitive property for distinguishing soils that originate from different locations.

http://youtu.be/5YNbvKMOfGw


Comparison of Soil

• In many forensic laboratories, forensic geologists will characterize and compare the mineral content of soils.

• Considering the vast variety of minerals and rocks

and the possible presence of artificial debris in soil, the forensic geologist is presented with many points of comparison between two or more specimens.

Comprehension assessment:Write down specific characteristics that you think you

should note when examining soil at the crime scene that may connect to a suspect, victim or other. (texture…


Collection of Soil

• Standard/reference (control) soil samples are to be collected at various intervals within a 100-yard radius of the crime scene, as well as the site of the crime, for comparison to the questioned soil.

• Soil found on the suspect, such as adhering to a shoe or garments, must not be removed from the items.

•Why?

• Instead, each object should be individually wrapped in paper and transmitted to the laboratory.

• Now do you know why we made 10 fold packages?


LAB - Glass

Lab – Each student will need to bring a inexpensive picture frame, preferably 8x10. Place 1 fingerprint on the glass (anywhere).

1.Each Student in the team will need “bunny suits” that covers head, need gloves and goggles.

2.Glass will be broken in a safe and supervised manner and not mixed with other broken glass.

3.Students will will have to put the glass back together, but-

1. Students will not put together their own glass2. Find the print and lift if possible (time, CSI box availability)3. Document/measure sizes, type of glass, fractures and overall condition.

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Soil Lab

Instructor must collect a small container full of 1 type of soil from campus, without students.

1. Teams (not as individuals) will be responsible for collecting 5 different samples of dirt from campus.

2. Each of the 5 samples is to be placed in a fold package/make sure you label the package.

3. Once in the lab, students will obtain a sample of the control sample and analyze. Compare the control sample to each of the 5 collected samples. Describe sight, smell, texture, type, wet/dry, anything that may be asked in court. Document your results in your packet.

4. Students should be very careful in using the microscopes in comparing samples. A very small amount is needed or the lens could get damaged.

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cte forensics/law & public safety 1-2

Documents

automobile paint comparison

forensic paint comparison

upper saddle river

new jersey

pearson higher education

paint binder formulations

common types of paint

trace evidence glass