Chapter 3: Physical Evidence

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Chapter 3Physical Evidence

• You can learn a lot by just watching.
• Yogi Berra, former New York Yankees catcher and
  sage

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Please Do Now
What is evidence? State 5 examples.
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Locards Exchange Principle

• Edmond Locard (1877-1966)
• Locard's Exchange Principle states that
  whenever two objects come into contact there is a
  transference of material between them.

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Types of Evidence

• Two general types
• Testimoniala statement made under oath also
  known as direct evidence or Prima Facie evidence
• Physicalany object or material that is relevant
  in a crime also known as indirect evidence.
  Examples are hair, fiber, fingerprints,
  documents, blood, soil, drugs, tool marks,
  impressions, glass.

Note This chapter will focus on physical
evidence
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Reliability of Eyewitness

• Factors
• Nature of the offense and the situation in which
  the crime is observed
• Characteristics of the witness
• Manner in which the information is retrieved
• Additional factors
• Witnesss prior relationship with the accused
• Length of time between the offense and the
  identification
• Any prior identification or failure to identify
  the defendant
• Any prior identification of a person other than
  the defendant by the eyewitness

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Eyewitness

• A police composite may be developed from the
  witness testimony by a computer program or
  forensic artist.
• Perception is reality.
• As a result of the influences in eyewitness
  memory, physical evidence becomes critical.

Facesa composite program by InterQuest
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Value of Physical Evidence

• Generally more reliable than testimonial
• Can prove that a crime has been committed
• Can corroborate or refute testimony
• Can link a suspect with a victim or with a crime
  scene
• Can establish the identity of persons associated
  with a crime
• Can allow reconstruction of events of a crime

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Physical Evidence

• It would be impossible to list all the objects
  that could conceivably be of importance to a
  crime.
• Almost anything can be Physical Evidence.
• Although you cannot rely on a list of categories,
  it is useful to discuss some of the most common
  types of physical evidence.
• The purpose of recognizing physical evidence is
  so that it can be collected and analyzed.
• It is difficult to ascertain the weight a given
  piece of evidence will have in a case as
  ultimately the weight will be decided by a jury.

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Common Types of Physical Evidence

• Blood, semen, and saliva
• Documents
• Drugs
• Explosives
• Fibers
• Fingerprints
• Firearms and ammunition
• Glass
• Hair
• Impressions
• Organs and physiological fluids

• Paint
• Petroleum products
• Plastic bags
• Plastic, rubber, and other polymers
• Powder residues
• Serial numbers
• Soil and minerals
• Tool marks
• Vehicle lights
• Wood and other vegetative matter

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Physical Evidence

• Blood, semen and saliva

• Documents

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Physical Evidence

• Drugs

• Explosives

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Physical Evidence

• Fibers

• Fingerprints

Silk fibers
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Physical Evidence

• Firearms and
• ammunition

• Glass

Refractive index
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Physical Evidence

• Hair

• Impressions

Dyed human hair
Impression foam
Hair shaft comparison
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Physical Evidence

• Organs and physiological fluids

• Paint

Car paint layers 300X
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Physical Evidence

• Petroleum products

• Plastic bags

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Physical Evidence

• Plastic, rubber and
• other polymers

• Powder residues

Powder residue test
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Physical Evidence

• Serial numbers

• Soil and minerals

Serial number restoration
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Physical Evidence

• Tool marks

• Vehicle lights

Honda Tail lights
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Physical Evidence

• Wood and other vegetative matter

Mixed pollen
Diatoms
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Common Types of Physical Evidence

• Blood, semen, and saliva
• Documents
• Drugs
• Explosives
• Fibers
• Fingerprints
• Firearms and ammunition
• Glass
• Hair
• Impressions
• Organs and physiological fluids

• Paint
• Petroleum products
• Plastic bags
• Plastic, rubber, and other polymers
• Powder residues
• Serial numbers
• Soil and minerals
• Tool marks
• Vehicle lights
• Wood and other vegetative matter

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Using Physical Evidence

• As the number of different objects linking an
  individual to a crime scene increases, so does
  the likelihood of that individuals involvement
  with the crime
• Also a person may be exonerated or excluded
  from suspicion if physical evidence collected at
  a crime scene is found to be different from
  standard/reference samples collected from that
  suspect

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Why Examine Physical Evidence?

• The examination of physical evidence by a
  forensic scientist is usually undertaken for
  identification or comparison purposes.
• Identification has, as its purpose, the
  determination of the physical or chemical
  identity of a substance with as near absolute
  certainty as existing analytical techniques will
  permit.
• A comparison analysis subjects a suspect specimen
  and a standard/reference specimen to the same
  tests and examinations for the ultimate purpose
  of determining whether or not they have a common
  origin.

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Identification

• to determine the physical or chemical identity
  with as near absolute certainty as existing
  analytical techniques will permit
• first requires the adoption of testing
  procedures that give characteristic results for
  specific standard materials
• Once these test results have been established,
  they may be permanently recorded and used
  repeatedly to prove the identity of suspect
  materials
• Second, the number and type of tests needed to
  identify a substance be sufficient to exclude all
  other substances

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Common Types of Identification

• The crime lab is often requested to identify
• Chemical composition of an illicit drug
• Gasoline in residues recovered from the debris of
  a fire, or the nature of explosive residues for
  example, dynamite or TNT
• Blood, semen, hair or wood - including a
  determination for species origin

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Comparison

• A comparative analysis has the important role
  of determining whether or not a suspect specimen
  and a standard/reference specimen have a common
  origin.
• Both the standard/reference and the suspect
  specimen are subject to the same tests.

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Forensic comparison

• A two step procedure
• First, combinations of select properties are
  chosen from the suspect and the
  standard/reference specimen for comparison.
• Second, once the examination has been completed,
  the forensic scientist must draw a conclusion
  about the origins of the specimens

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Role of Probability in Forensic Comparison

• To comprehend the evidential value of a
  comparison, one must appreciate the role that
  probability has in ascertaining the origins of
  two or more specimens
• Probability the frequency of occurrence
• of an event
• Easy to establish the probability of flipping a
  
• coin
• Exact probability is impossible to define with
  many
• analytical processes

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Probability
For example Blood Factors Frequency A
26 EsD 85 PGM 22
2 What is the probability of someone having all
three factors?
Using the product rule
0.26 X 0.85 X 0.02 0.00442 which is
ONLY 0.442 or 1OO or 1 out of 226 people
.442
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Classifying Characteristics

• Individual Characteristics
• Properties of evidence that can be
  attributed to a common source with an
  extremely high degree of certainty
• Class Characteristics
• Properties of evidence that can only be
  associated with a group and never with a
  single source

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Individual Characteristics

• In all cases, it is not possible to state with
  
• mathematical exactness the probability
• that the specimens are of common origin.
• It can only be concluded that this
• probability is so high as to defy
• mathematical calculations or human
• comprehension.

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Evidence Characteristics

• Class characteristicsEvidence common to a group
  of objects or persons
• Individual characteristicsEvidence can be
  identified with a particular person or a single
  source with an extremely high degree of
  probability

Blood DNA Typing
Fingerprints
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Examples of Individual Characteristics

• the matching ridge characteristics of two
  fingerprints
• the comparison of random striation markings on
  bullets or tool marks
• the comparison of irregular and random wear
  patterns in tire or footwear impressions
• the comparison of handwriting characteristics
• the fitting together of the irregular edges of
  broken objects in the manner of a jigsaw puzzle
• matching sequentially made plastic bags by
  striation marks running across the bags

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Class vs Individual Evidence
Which examples do you think could be individual
evidence?
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Class vs Individual Evidence

• These fibers are class evidencethere are
  millions like them.

• The large piece of glass fits to the bottleit is
  individual evidence

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Class vs Individual Evidence

• This tape is class evidencebut it could be
  individual evidence if the striations of the tear
  match.

• it is individual evidence the dental work on the
  teeth can be used to identify the person

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Class vs Individual Evidence

• This tire track is class
• evidence, as it can be
• linked to a class of tire
• but it could be individual
• evidence if there are
• unique impressions.

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Class Characteristics

• Frequently forensic scientists cannot relate
  physical evidence to a common origin with a high
  degree of certainty
• Evidence is said to possess class
  characteristics when it can be associated only
  with a group and never with a single source.
• Again, probability is a determining factor.
• Nevertheless, the high diversity of class
  evidence in our environment makes their
  comparison very significant in the context of a
  criminal investigation.

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Class Evidence

• A weaknesses of forensic science is the
  inability of the examiner to assign exact or even
  approximate probability values to the comparison
  of most class physical evidence.
• For example, what is the probability that a
  nylon fiber originated from a particular sweater,
  or that a paint chip came from a suspect car in a
  hit and run?
• There are very few statistical data available
  from which to derive this information, and in a
  mass-produced world, gathering this kind of data
  is increasingly elusive.

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Class Evidence

• One of the primary endeavors of forensic
  scientists must be to create and update
  statistical databases for evaluating the
  significance of class physical evidence.
• Most items of physical evidence retrieved at
  crime scenes cannot be linked definitively to a
  single person or object.
• The value of class physical evidence lies in
  its ability to provide corroboration of events
  with data that are, as nearly as possible, free
  of human error and bias.

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Class Evidence

• The chances are low of encountering two
  indistinguishable items of physical evidence at a
  crime scene that actually originated from
  different sources.
• When one is dealing with more than one type of
  class evidence, their collective presence may
  lead to an extremely high certainty that they
  originated from the same source.
• Finally, the contribution of physical evidence
  is ultimately determined in the courtroom.

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Crossing Over

• Crossing over the line from class to individual
  does not end the discussions.
• How many striations are necessary to
  individualize a mark to a single tool and no
  other?
• How many color layers individualize a paint
  chip to a single car?
• How many ridge characteristics individualize a
  fingerprint?
• How many handwriting characteristics tie a
  person to a signature?
• These are all questions that defy simple
  answers and are the basis of arguments.

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Natural vs. Evidential Limits

• There are practical limits to the properties
  and characteristics the forensic scientist can
  select for comparison.
• Modern analytical techniques have become so
  sophisticated and sensitive that natural
  variations in objects become almost infinite.
• Carrying natural variations to the extreme, no
  two things in this world are alike in every
  detail.
• Evidential variations are not the same as natural
  variations.
• Distinguishing variations of evidential use from
  natural variations is not always an easy task.

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Forensic Databases

• The ultimate contribution a criminalist can
  make is
• The crime lab is on the forefront of the
  investigation seeking to identify perpetrators
• computerized databases link all 50 states and
  those that link police agencies throughout the
  world

to link a suspect to a crime through comparative
analysis
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Forensic Databases

• Integrated Automated Fingerprint Identification
  System (IAFIS)
• a national fingerprint and criminal history
  system maintained by the FBI

60 million prints on file
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Forensic Databases

• Combined DNA Index System (CODIS)
• enables federal, state, and local crime
  laboratories to electronically exchange and
  compare DNA profiles - maintained by the FBI

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Forensic Databases

• National Integrated Ballistics Information
  Network (NIBIN)
• Allows firearm analysts to acquire, digitize, and
  compare markings made by a firearm on bullets and
  cartridge casings
• maintained by the Bureau of Alcohol, Tobacco,
  Firearms and Explosives (ATF)

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Forensic Databases

• International Forensic Automotive Paint Data
  Query (PDQ)
• contains chemical and color information
  pertaining to original automotive paints
• maintained by the Forensic Laboratory Services
  of the Royal Canadian Mounted Police

Cross section of Automobile paint
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Forensic Databases

• Shoeprint image capture and retrieval (SICAR)
• shoeprint database
• computer retrieval system
• - not maintained by a
• government agency

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Reconstruction

• The method used to support a likely sequence of
  events by the observation and evaluation of
  physical evidence, as well as statements made by
  those involved with the incident, is referred to
  as reconstruction.
• Crime-scene reconstruction relies on the
  combined efforts of medical examiners,
  criminalists, and law enforcement personnel to
  recover physical evidence and to sort out the
  events surrounding the occurrence of a crime.

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The Role of Physical Evidence

• The physical evidence left behind at a crime
  scene plays a crucial role in reconstructing the
  events that took place surrounding the crime.
• Although the evidence alone does not describe
  everything that happened, it can support or
  contradict accounts given by witnesses and/or
  suspects.
• Information obtained from physical evidence can
  also generate leads and confirm the
  reconstruction of a crime to a jury.
• The collection and documentation of physical
  evidence is the foundation of a reconstruction.

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Reconstruction

• Physical Evidence is used to answer questions
  about
• what took place
• how the victim was killed
• number of people involved
• sequence of events
• A forensic scientist will compare the questioned
  or unknown sample with a sample of known origin.

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Summing It Up

• Reconstruction is a team effort that involves
  putting together many different pieces of a
  puzzle.
• The right connections have to be made among all
  the parts involved so as to portray the
  relationship among the victim, the suspect, and
  the crime scene.
• If successful, reconstruction can play a vital
  role in aiding a jury to arrive at an appropriate
  verdict.
• The recognition, collection, and analysis of
  physical evidence is the foundation to successful
  reconstruction, but only part of the process.

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Types of Physical Evidence

• Transient Evidencetemporary easily changed or
  lost usually observed by the first officer at
  the scene
• Pattern Evidenceproduced by direct contact
  between a person and an object or between two
  objects
• Conditional Evidenceproduced by a specific event
  or action important in crime scene
  reconstruction and in determining the set of
  circumstances or sequence within a particular
  event
• Transfer Evidenceproduced by contact between
  person(s) or object(s), or between person(s) and
  person(s)
• Associative Evidenceitems that may associate a
  victim or suspect with a scene or each other ie,
  personal belongings
• Lee and Labriola in Famous Cases, 2001

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Examples of Transient Evidence

• Odorputrefaction, perfume, gasoline, urine,
  burning, explosives, cigarette or cigar smoke
• Temperaturesurroundings, car hood, coffee, water
  in a bathtub, cadaver
• Imprints and indentationsfootprints, teeth marks
  in perishable foods, tire marks on certain
  surfaces
• Markings

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Examples of Pattern Evidence

• Pattern Evidencemost are in the form of
  imprints, indentations, striations, markings,
  fractures or deposits.

• Clothing or article distribution
• Gun powder residue
• Material damage
• Body position
• Tool marks
• Modus operandi

• Blood spatter
• Glass fracture
• Fire burn pattern
• Furniture position
• Projectile trajectory
• Tire marks or skid marks

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Examples of Conditional Evidence

• Lightheadlight, lighting conditions
• Smokecolor, direction of travel, density, odor
• Firecolor and direction of the flames, speed of
  spread, temperature and condition of fire
• Locationof injuries or wounds, of bloodstains,
  of the victims vehicle, of weapons or cartridge
  cases, of broken glass

• Vehiclesdoors locked or unlocked, windows opened
  or closed, radio off or on (station), odometer
  mileage
• Bodyposition, types of wounds rigor, livor and
  algor mortis
• Scenecondition of furniture, doors and windows,
  any disturbance or signs of a struggle

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Classification ofEvidence by Nature

• Biologicalblood, semen, saliva, sweat, tears,
  hair, bone, tissues, urine, feces, animal
  material, insects, bacterial, fungal, botanical
• Chemicalfibers, glass, soil, gunpowder, metal,
  mineral, narcotics, drugs, paper, ink, cosmetics,
  paint, plastic, lubricants, fertilizer
• Physicalfingerprints, footprints, shoe prints,
  handwriting, firearms, tire marks, tool marks,
  typewriting
• Miscellaneouslaundry marks, voice analysis,
  polygraph, photography, stress evaluation,
  psycholinguistic analysis, vehicle identification

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Forensic Investigations

• Include some or all of these seven major
  activities
• 1. Recognitionability to distinguish important
  evidence from unrelated material
• Pattern recognition
• Physical property observation
• Information analysis
• Field testing
• 2. Preservationcollection and proper
  preservation of evidence

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Investigations

• 3. Identificationuse of scientific testing
• Physical properties
• Chemical properties
• Morphological (structural) properties
• Biological properties
• Immunological properties
• 4. Comparisonclass characteristics are measured
  against those of known standards or controls if
  all measurements are equal, then the two samples
  may be considered to have come from the same
  source or origin.

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Investigations

• 5. Individualizationdemonstrating that the
  sample is unique, even among members of the same
  class
• 6. Interpretationgives meaning to all the
  information
• 7. Reconstructionreconstructs the events of the
  case
• Inductive and deductive logic
• Statistical data
• Pattern analysis
• Results of laboratory analysis
• Lee, Dr. Henry. Famous Crimes, 2001