FORENSIC SCIENCE
Physical Evidence
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PHYSICAL 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
Criminology
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 Evidence
in the Courtroom
1993 Daubert v. Dow
1923
Admissibility is determined
Frye v. United States
by:
the theory or
Scientific evidence is  Whether
technique can be tested
allowed into the
 Whether the science has been
offered for peer review
courtroom if it was
generally accepted  Whether the rate of error is
acceptable
by the scientific
 Whether the method at issue
community.
enjoys widespread acceptance.
 Whether the opinion is relevant
to the issue
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Probative Value
of 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 Evidence
Glass
• fractures
• density
• refractive index
Soil
• characteristic
• types
• location
Sand
• characteristic
• types
• location
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INVESTIGATIONS
Observation
Experimentation
Note Taking
Recording data and
results
Drawing conclusions-putting it all together
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GLASS
Glass
A. 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
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GLASS (cont)
B. Determining Physical Characteristics
1. Density= mass divided by volume
2. Refractive index--the bending of light waves
due to a change in velocity.
3. Fractures
a. 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)
C. Used as Evidence
1. 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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SOIL
Soil
A. Definition--the naturally deposited
material that covers the earth’s surface
and is capable of supporting plant growth
B. The Earth
1. 75%--oceans, seas and lakes
2. 15%--deserts, polar ice caps
and mountains
3. 10%--suitable for agriculture
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Soil (cont)
C. Formation
1. Living matter--plants, animals and microorganisms
2. Climate
3. Parent materials
4. Relief--slope and land form
5. Time
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Soil (cont)
D. Profile
– Topsoil
– Subsoil
– Parent material
E. Composition
–
–
–
–
Sand
Silt
Clay
Organic matter
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Soil (cont)
F. Nutrients--macro
1.
2.
3.
4.
5.
6.
Nitrogen
Phosphorus
Potassium
Calcium
Magnesium
Sulfur
G. Nutrients--micro
1.
2.
3.
4.
5.
6.
7.
Manganese
Iron
Boron
Copper
Zinc
Molybdenum
Chlorine
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Soil (cont)
H. Soil types in the United States
1. 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
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SOIL (cont)
I. Used as Evidence
1. 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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SAND
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.)
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 Examples
Great Salt Lake
Its unique
characteristic is
the very round
shaped grains.
Magnified 30x using a dissecting
stereomicroscope.
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Sand Examples
Black Sands of Hawaii
Magnified 30x using a dissecting
stereomicroscope.
Its unique
characteristic
includes the black
grains made of
basalt lava from
volcanic eruptions.
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Sand Evidence
“In every grain of sand is a story of earth.” --Rachel
Carson
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
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Unusual “Physical Evidence”
Crazy 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 6year 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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