FORENSIC SCIENCE

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FORENSIC SCIENCE

• Glass and Soil Evidence

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Physical Evidence

• Glass
• fractures
• density
• refractive index
• Soil
• characteristic
• types
• location
• Sand
• characteristic
• types
• location

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• Glass
• Glass particles can be found at various crime
  scenes, such as breaking and entering, hit and
  run, vandalism, or murder. 
• Glass at a crime scene is analyzed to determine
  its color, surface characteristics, tint,
  thickness, density, chemical composition, and
  refractive index (RI).
• The results of the tests provide clues about the
  crime and help investigators connect the evidence
  to a suspect or other object used in a crime,
  such as matching glass from a crime scene to a
  headlight to a suspects car.

Magnified image of glass fragments
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How do forensic scientists matchsamples of glass?

• Physical examination
• Some important features to note are edge
  thickness, color, and the presence of any labels
  or imprints on the glass. A black-light lamp may
  be used to check for repairs as hairline cracks
  will glow under ultraviolet light.
• Thickness- Glass thickness is generally a
  function of its application. Glass from a light
  bulb is going to be thinner than a pane of window
  glass. The glass used in a picture frame is
  generally not subject to gusts of wind, so it
  will be thinner than glass used in a window.
  Glass used in a door is generally even thicker,
  to withstand the forces applied as a result of
  frequent opening and closing (and sometimes
  slamming!).

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GLASS (cont)More Physical Characteristics

• Density The formula for density is mass/volume,
  and the density of two pieces of glass will
  always be the same if they come from the same
  source.
• Refractive index--the bending of light waves due
  to a change in velocity. Any object that
  transmits light has its own refractive index,
  which is a measure of how much the
• object slows the speed of light. When light
  passes through any medium, it is slowed down. The
  denser the medium, the slower the light travels.
  The FBI has a database of refractive index values
  for approximately 2000 different types of glass,
  allowing forensic scientists the ability to
  identify samples.

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The Becke line

• Every liquid has its own refractive index. If a
  piece of glass is placed in a liquid with a
  different refractive index, an outline of the
  glass is clearly visibleknown as the Becke line.
  However, if a piece of glass is placed in a
  liquid with the same refractive index, the Becke
  line will disappear and the glass will
• seem to disappear. This is because the glass
• bends light at the same angle as the liquid.

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Fractures
- When an object broken, torn, or cut, two unique
edges are formed, which are referred to as
fracture lines These edges can be compared by the
naked eye or with microscopes to see if they fit
together, which indicates that they may have been
part of the same object at one time.
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Radial Glass fracture

• The radial fractures are produced first and
  always form on the side of the glass opposite to
  where the impact originated. Radial fractures
  look like spider webs that spread outward from
  the impact hole. A radial fracture will always
  terminate into an existing fracture

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Concentric Glass fracture

• Concentric fractures form next, and these lines
  encircle the bullet hole.
• Concentric fractures always start on the same
  side as that of the destructive force.
• The direction from which a bullet was fired can
  be
• determined by comparing
• the size of the entrance hole to that of the exit
  hole. Exit holes are always
• larger

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Chemical Composition

• The difference between types of glass can be due
  to the chemical composition of the glass itself
  or differences in how the glass was manufactured.
• Most glass is made from silicon dioxide (SiO2),
  the primary ingredient in sand, which has been
  heated above its melting point of1600C. Various
  substances are then added, depending on what type
  of glass is desired.
• Soda and Lime are added to make it easier to make
  glass like windows, and containers
• Boron oxide (B2O3) is used to make Pyrex
  glassware because it expands and contracts easier
  when heated.
• - Potassium oxide (K2O) is used To make
  eye glasses. This imparts hardness to the
  glass.

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Was the light onor off?

• Light bulbs do not actually burn, but rather,
  glow as the tungsten filament becomes very hot
  due to the resistance that the electrons
  encounter as they pass through the wire filament.
• In a properly functioning light bulb, the
  glowing filament is inside of the bulb filled
  with a noble gas such as argon.
• But if the filament is glowing when the bulb is
  broken, it will immediately react with oxygen in
  the air and break in half. This will form a thick
  layer of yellowish-white tungsten oxide on the
  filament due to the reaction of the tungsten with
  oxygen. If the presence of tungsten oxide on the
  filament is found, then it can be proven that the
  bulb was on when the accident occurred.

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GLASS

• Glass Common Types
• 1. Soda-lime--used in plate and window glass,
  glass containers, and electric light bulbs ,
  easier to mold into objects
• 2. Soda-lead--fine table ware and art objects
• 3. Borosilicate--heat resistant, like Pyrex
• 4. Silica--used in chemical ware, heat resistant
• 5. Tempered--used in side windows of cars,
  quickly heated and cooled to improve strength
• 6. Laminated--used in the windshield of most
  cars, plastic is sandwiched between layers of
  glass

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GLASS

• 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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Collection and Preservation of Glass Evidence

• - Pieces of clothing or shoes which contain glass
  evidence should be placed in paper and collected.
• - For hit and run cases, all glass close to the
  crime scene should be collected and preserved, as
  well as those farther away since the car
  continued moving.
• - Smaller glass fragments should be placed in
  paper, or cans. They should then be sealed and
  labeled.
• - Larger glass fragments should be placed within
  boxes. The pieces should be separated with
  cotton or other soft material to prevent damage
  to the evidence. They should be sealed and
  labeled as well.

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Dust Dirt

• Dust, dirt, or sand evidence can reveal where a
  person has traveled and may be picked up at a
  crime scene or left behind.
• Investigators examine the samples for chemical
  composition, pollen, plant material, and other
  organic matter to find links to a specific crime
  scene.

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SOIL

• Soil
• A. Definition--the naturally deposited
  material that covers the earths 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. Nitrogen
• 2. Phosphorus
• 3. Potassium
• 4. Calcium
• 5. Magnesium
• 6. Sulfur

• G. Nutrients--micro
• 1. Manganese
• 2. Iron
• 3. Boron
• 4. Copper
• 5. Zinc
• 6. Molybdenum
• 7. 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
• Its unique characteristic includes the black
  grains made of basalt lava from volcanic
  eruptions.

Magnified 30x using a dissecting
stereomicroscope.
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Sand EvidenceIn 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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Paint

• Most often found in
• 1. Hit and run
• 2. burglary cases
• Dried paint is composed of 2 things
• Pigment
• color and opacity
• made of organic and inorganic compounds
• Binder
• provides the support medium for the pigments
• polymeric substance
• Other additives that are dissolved or suspended
  in a solvent
• After the paint has been applied, the solvent
  evaporates, leaving the hard polymer binder and
  pigments behind

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Forensic Examination of Paint

• Stereoscopic microscope
• Side by side comparison
• Color, surface texture, color layer sequence
• Depends on
• uniqueness of each layer with respect to its
  color and texture
• How often (frequency) the particular combination
  of colors occurred
• Problems?
• Most paint specimens will not have a layered
  structure
• Usually dont have paint chips that can
  physically fitted together

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Forensic Examination (cont.)

• Examine the chemical composition
• Must include a chemical analysis of the pigments
  and/or its binder
• Provides additional points of comparison
• There are more than 100 automobile production
  plants in the USeach with their own supplier(s)

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Forensic Examination (cont.)

• Once the comparison is completed it is then time
  to assess the significance of the findings
• How certain can one be that 2 similar paints did
  indeed come from the same surface?
• 1974- the Law Enforcement Standards Laboratory at
  the the National Institute of Standards and
  Technology collected and disseminated to crime
  laboratories auto paint color samples from US
  domestic passenger cars

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Unusual Physical EvidenceCrazy 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 couples 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.