Physical Evidence

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Physical Evidence

• Objects that can establish that a crime has been
  committed

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Definition of Physical Evidence

• Physical evidence encompasses any and all
  objects that can establish that a crime has been
  committed or can provide a link between a crime
  and its victim or a crime and its perpetrator.

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Common Types of Physical Evidence

• Blood, Semen, and Saliva these are subject to
  serological and biochemical analysis
• Documents any handwriting, typewriting, ink,
  indented writing, obliterations, burned or
  charred documents
• Drugs
• Explosives any device with an explosive charge
  and any item that may contain the explosive
  residue
• Fibers any fiber that may show cross-transfer
  between object and/or persons
• Fingerprints latent and visible

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Common Types (cont.)

• Firearms and Ammunition
• Glass particles that may show cross-transfer or
  panes that may have bullet holes
• Hair animal or human hair showing
  cross-transfer
• Impressions tire markings, shoe prints,
  depressions in soil, glove or fabric impressions,
  bite marks in skin or food
• Organs and Physiological Fluids body organs and
  fluids are tested for drugs and poisons
• Paint particles showing cross-transfer (auto
  accidents)

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Common Types (cont.)

• Petroleum Products gas residues from arson
  scenes, grease or oil stains
• Plastic bags usually for drug residues
• Plastic, Rubber or other Polymers- cross-transfer
• Powder Residues firearm discharge residues
• Serial Numbers stolen property submitted to lab
  for serial number restoration
• Soil and Minerals cross-transfer (esp. soil
  embedded in shoes)

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Common Types (cont.)

• Tool Marks any object suspected of having an
  impression of another tool in it (ex. crowbar
  may leave marks on a windowsill in a break-in)
• Vehicle Lights examination of vehicle lights
  can determine whether they were on or off at the
  time of impact
• Wood or other Vegetative Matter cross-transfer

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Identification of a Substance

• Identification process of determining a
  substances physical or chemical identity

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Identification (cont.)

• Drug analysis, species determination, and
  explosive residue analysis are typical tests
  performed to determine identity
• Common standard tests are used to determine
  identity. There are standard tests for most
  drugs, blood species of origin and explosive
  materials.
• Some materials can be determined with one test
  while others may require several tests

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Comparison

• Comparison--process of determining whether two or
  more objects have a common origin

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Comparison Cont

• Scientists will compare the control and suspect
  specimen to determine if they are the same
• This type of analysis can assist in placing a
  suspect at the scene
• Two-step Procedure
• combos of select properties of the control and
  suspect specimens are chosen for comparison
• once the examination is completed, the forensic
  scientist will render a conclusion as to how
  closely related the two specimens are

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Comparison Cont

• If any of the selected properties are not alike,
  the scientist will declare that the two items are
  not from the same source. However, if all of the
  selected properties match, they still may not be
  able to conclude that the two specimens are from
  the same source with 100 accuracy.
• Therefore, usually only the probability that two
  specimens came from the same source is
  given

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Individual Characteristics

• Individual Characteristics Properties of
  evidence that can be attributed to a common
  source with an extremely high degree of certainty

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Individual Characteristics
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Individual Characteristics
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Individual Characteristics Cont

• Examples DNA, fingerprint ridges,
  grooves/striations on a bullet or toolmark,
  irregular and random wear patterns on tire or
  shoe impressions, handwriting characteristics,
  fitting together pieces of broken objects,
  matching the striations in sequentially made
  plastic bags, etc.
• The probability of two people having the same
  fingerprints is 0.0000000000000000000000000000000
  000000000000000000000000000006.

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Class Characteristics

• Class Characteristics Properties of evidence
  that can only be associated with a group and
  never with a single source

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Class Characteristics
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Class Characteristics Cont

• Examples new factory painted cars with only two
  layers of paint, blood to a certain degree
• Uses of Class Characteristics are usually to
  corroborate the events with data that are free of
  human bias

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Class v Individual Characteristics
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Class or Individual?

• DNA Evidence

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Class or Individual?

• Boot Print

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Class or Individual?

• Fiber Evidence

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Class or Individual?

• Fingerprint

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Class or Individual?

• Hair

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Class or Individual?

• Shotshell Casings