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FORENSIC SCIENCEFORENSIC SCIENCE

Physical Evidence

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PHYSICAL EVIDENCEPHYSICAL EVIDENCE

You can lead a jury to the truth but you can’t make them believe it. Physical evidence cannot be intimidated. It does not forget. It doesn’t get excited at the moment something is happening--like people do. It sits there and waits to be detected, preserved, evaluated and explained. This is what physical evidence is all about. In the course of the trial, defense and prosecuting attorneys may lie, witnesses may lie, the defendant certainly may lie. Even the judge may lie. Only the evidence never lies. --Herbert Leon MacDonell, The Evidence Never Lies

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Criminalistics vs Criminalistics vs CriminologyCriminology

Criminalistics is the scientific examination of physical evidence for legal purposes.

Criminology includes the psychological angle, studying the crime scene for motive, traits, and behavior that will help to interpret the evidence.

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Scientific EvidenceScientific Evidencein the Courtroomin the Courtroom

1923

Frye v. United States

Scientific evidence is allowed into the courtroom if it was generally accepted by the scientific community.

1993 Daubert v. DowAdmissibility is determined

by: Whether the theory or

technique can be tested Whether the science has been

offered for peer review Whether the rate of error is

acceptable Whether the method at issue

enjoys widespread acceptance. Whether the opinion is relevant

to the issue

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Probative ValueProbative Valueof Physical Evidenceof Physical Evidence

Legally, probative value is the level at which evidence provides proof of the crime.

Associative value is used to place a suspect at a crime.

Product rule--how often something occurs in nature or the “real world”.

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Physical EvidencePhysical Evidence

Glass• fractures• density• refractive index

Soil• characteristic• types• location

Sand• characteristic• types• location

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INVESTIGATIONSINVESTIGATIONS

ObservationExperimentationNote TakingRecording data and

resultsDrawing conclusions--

putting it all together

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GlassA. Common Types

1. Soda-lime--used in plate and window glass, glass containers, and electric light bulbs

2. Soda-lead--fine table ware and art objects

3. Borosilicate--heat resistant, like Pyrex

4. Silica--used in chemical ware

5. Tempered--used in side windows of cars

6. Laminated--used in the windshield of most cars

GLASSGLASS

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GLASS (cont)GLASS (cont)

B. Determining Physical Characteristics1. Density= mass divided by volume

2. Refractive index--the bending of light waves due to a change in velocity.

3. Fracturesa. radial fractures--straight lines that come off the

point of impact

b. concentric fractures--circular lines around the point of impact

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GLASS (cont)GLASS (cont)

C. Used as Evidence1. Class characteristic--the type of glass

may be evident at the crime scene

2. Individual characteristic--can piece the glass in the piece of evidence from the crime scene

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SOILSOIL

SoilA. Definition--the naturally deposited material that covers the earth’s surface and is capable of supporting plant growthB. The Earth

1. 75%--oceans, seas and lakes2. 15%--deserts, polar ice caps and mountains3. 10%--suitable for agriculture

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C. Formation

1. Living matter--plants, animals and microorganisms

2. Climate

3. Parent materials

4. Relief--slope and land form

5. Time

Soil (cont)

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Soil (cont)Soil (cont)

D. Profile– Topsoil– Subsoil– Parent material

E. Composition– Sand– Silt– Clay– Organic matter

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F. Nutrients--macro1. Nitrogen

2. Phosphorus

3. Potassium

4. Calcium

5. Magnesium

6. Sulfur

G. Nutrients--micro1. Manganese

2. Iron

3. Boron

4. Copper

5. Zinc

6. Molybdenum

7. Chlorine

Soil (cont)Soil (cont)

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H. Soil types in the United States1. Pedalfers--soils rich in clay, iron oxides, and

quartz fragments where rainfall exceeds 65 centimeters per year; mostly the eastern half of the country

2. Pedocals--soils with less clay and rich in calcium carbonate where rainfall less than 65 centimeters per year; the western half of country except for the Pacific coast region

Soil (cont)Soil (cont)

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SOIL (cont)SOIL (cont)

I. Used as Evidence1. Class characteristic--the type of soil may

have similar characteristics at the primary and/or secondary crime scene, on the suspect or on the victim

2. Individual characteristic--only if the soil has an unusual characteristic such as pollen, seeds, vegetation, or fragments.

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SANDSAND

Sand is the term applied to natural particles with a grain diameter between 1/16mm and 2 mm.

Its color and contents is dependent upon the parent rock and surrounding plant and animal life.

(The photo on the right shows color differences in sand from six locations around the world.)

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SAND (cont.)SAND (cont.)

Types 1. Continental sands--formed from weathered

continental rock, usually granite

2. Ocean Floor sands--formed from volcanic material, usually basalt

3. Carbonate sands--composed of various forms of calcium carbonate

4. Tufa sands--formed when calcium ions from underground springs precipitate with

carbonate ions in salt water in a salt lake

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Sand ExamplesSand Examples

Great Salt Lake

Its unique characteristic is the very round shaped grains.

Magnified 30x using a dissecting stereomicroscope.

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Sand ExamplesSand Examples

Black Sands of Hawaii

Its unique characteristic includes the black grains made of basalt lava from volcanic eruptions.

Magnified 30x using a dissecting stereomicroscope.

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Unusual “Physical Evidence”Unusual “Physical Evidence”Crazy CriminalsCrazy Criminals

Donna Clark, 26, and Paul Kramer, 31, face charges in New Jersey. Clark allegedly grabbed $216 worth of film and walked out of a drugstore. The couple’s names were provided by their 6-year old son, who was in the store at the time but who was forgotten by the couple as they made their getaway.

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Sand EvidenceSand Evidence“In every grain of sand is a story of earth.” --Rachel “In every grain of sand is a story of earth.” --Rachel

CarsonCarson

Class characteristic--the type of sand may have similar characteristics at the primary and/or secondary crime scene, on the suspect or on the victim

Individual characteristic--only if the sand has an unusual characteristic