CRIMINALISTICS CHAPTER 3

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CRIMINALISTICS CHAPTER 3

• PHYSICAL EVIDENCE

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PHYSICAL EVIDENCE

• Impossible to list all items that could be
  important at crime scene\
• Practicle to list those that scientific
  examination can yield significant results
• Investigator needs to be familiar with
• Recognition Collection analyses
• Laboratory procedures and capabilities

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COMMON TYPES OF PHYSICAL EVIDENCE

• Lists and definitions or examinations

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BLOOD, SEMEN SALIVA

• All suspected saples
• Liquid or dried
• Animal or human
• Subjected to serological examination (DNA) to
  determine
• Identity
• Origin

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DOCUMENTS

• Handwriting or Typewriting
• Determine authenticity or Source
• Related Items
• Paper
• Ink
• Indented writing
• Obliterations
• Burned or Charred documents

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DRUGS

• Controlled substances seized in violation of the
  law
• Sale
• Distribution
• Manufacture
• Possession

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EXPLOSIVES

• Devices containing explosive charge
• Residue from scene of explosion to examine for
  suspected explosive charge

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FIBERS

• Natural or synthetic fibers
• Transfer may be helpful in establishing
  relationship between objects/persons

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FINGERPRINTS

• Latent or other prints
• Establish identity
• Place at scene

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FIREARMS

• Firearms, Projectiles, cartridges
• Identify
• Compare
• To other exemplars
• To firearms
• Firearms residue
• Present?
• Distance angle

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GLASS

• Glass particles or fragments
• Transfer evidence
• Window panes with holes
• Sequence origin
• Broken windows
• Characteristics

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HAIR

• Animal or human
• Origin
• Race
• Body area
• Comparison
• Root present
• DNA

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IMPRESSIONS

• Tire or Shoe prints in soft material
• Fabric Impressions
• Bite marks

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PAINT

• Liquid or dried
• Transfer from one surface to another
• Identification
• Comparison

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PETROLEUM PRODUCTS

• Arson
• Residues identified at fire scene (accelerants)
• Oil or grease stains
• Comparisons to place at scene

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PLASTIC BAGS

• Identification
• Comparison to known
• Fracture match

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POLYMERS

• Plastic, Rubber, etc
• Identification
• Comparison to objects at scene

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SERIAL NUMBERS

• Usually falls under firearms
• Stolen property
• Defaced serial numbers restored

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SOIL AND MINERALS

• Link a person or object to location
• Examples
• Soil found on clothing or vehicles
• Soil found on tools

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TOOL MARKS

• Usually under firearms
• Impressions made by tool

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LIGHTS

• Mainly vehicle
• Conducted to determine on/off during crash

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WOOD

• Other vegetative material
• Comparison
• To link suspect to scene

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PHYSICAL EVIDENCE

• IDENTIFICATION
• COMPARISON

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MATHEMATICAL PROBABILITY

• Underlies virtually every human action
• Based on idea that the outcome of an event can be
  logically estimated
• Estimate based on known conditions, past
  performance , experience with similar events
• Familiar example (coin toss)

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PROBABILITY

• Blood as example
• Four major types
• O 40 820
• A 40 820
• B 15 320
• AB 5 120
• Any blood stain must be one of these types

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Probability

• Significance
• Probability of occurrence of different types
• Ex O is 8 times more common than AB
• If O found fewer people eliminated than if AB is
  found
• AB sample is therefore higher quality evidence
  than type O

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Probability

• The greater the frequency of occurance the less
  significance attached
• Must also consider concept of Mutually Exclusive
• Events that by nature preclude other events
• Not possible for individual to have two types
• Therefore if type A found at scene the blood did
  not come from person with any other type

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PROBABILITY

• Some forms of physical evidence do not lend
  themselves to statistical evaluation
• Example Do not know statistical probability of a
  particular configuration of a toolmark
• Value must be estimated base on experience
• Must form an opinion as to value of evidence

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PROBABILITY

• Experience has shown that microscopic
  relationships between the impression and the tool
  are so specific to be unique
• The basis of the opinion must be experience that
  equips the examiner to note the unique points
  that distinguish the item from a larger body of
  occurances

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IDENTIFICATION

• Definition
• The determination of the physical or chemical
  identity of a substance with as near absolute
  certainty as existing analytical techniques will
  permit

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IDENTIFICATION

• EXAMPLES
• Suspected drug sample identified to contain
  cocaine
• Residues from a fire identified to contain
  gasoline
• Sample found at scene identified as blood
• May determine species
• Vegetable material identified as type of wood

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IDENTIFICATION

• 1.Adoption of standard testing procedures
• must give characteristic results for standard
  testing materials
• Testing permanently established
• used to establish identity
• test results must be same on unknown as on a
  known sample

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IDENTIFICATION

• 2. The number and type of tests must be
  sufficient to exclude all other substances
• Must devise an analytical scheme that will
  eliminate all but one substance
• If identify white powder as cocaine must exclude
  every other drug

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IDENTIFICATION

• No simple rules as to what constitutes thorough
  and foolproof analytical scheme
• Each type of evidence requires different type of
  tests
• Some may be identified with one test, some may
  require many
• Little or no control over the quality or quantity
  of samples submitted

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IDENTIFICATION

• The forensic scientist must conclude in many
  cases
• What point the analyses is concluded
• The criteria for positive identification
• Conclusion beyond reasonable doubt for court
• Most disciplines have SOP

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COMPARISON

• OF KNOWN AND UNKNOWN

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COMPARISON

• Definition
• An analysis that subjects a suspect speciman 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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COMPARISON

• Examples
• Place a suspect at scene by noting similarities
  between hair found at scene to known hair of
  suspect
• Similar to or consistent with and could have a
  common origin

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COMPARISON

• Examples
• Place vehicle at scene of hit and run by noting
  similarities between paint found on victim
  clothing and known paint from vehicle
• Chemical and physical property match
• could have common origin
• Fracture match
• have a common origin

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COMPARISON

• Forensic comparison two step process
• 1. Combinations of select properties are chosen
  from the suspect and the standard/reference
  specimen for comparison
• How many properties are chosen depends on the
  type of material
• Overriding consideration must be the ultimate
  evidential value of the conclusion

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COMPARISON

• 2. When examination is completed the examiner
  must be prepared to render a conclusion with
  respect to the comparison
• Do they come from same source
• If one property does not agree, no common origin
• If all properties compared agree are they from
  common origin (not necessarily)

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COMPARISON

• Physical match
• The most definite point of comparison between
  objects
• Example point of screwdriver and shaft from
  which it broke
• Any item that suggests a rip, tear, or breakage
  should lead to a search for its counterpart

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INDIVIDUAL CHARACTERISTICS

• Definition
• Evidence that can be associated with a common
  source with a high degree of probability
• Examples
• Matching ridge characteristics of two
  fingerprints
• Matching striations on bullets
• Matching irregular and random wear patterns on
  footwear

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INDIVIDUAL

• Not possible to state with mathematical exactness
  the probability that specimens are of common
  origin. (exception DNA)
• Conclusion that probability is so high as to defy
  mathematical calculations or human comprehension
• INDIVIDUAL
• Example Fingerprints
• Several mathematical models proposed
• One model probability of two individuals with
  same fingerprint 1 x 10 followed by 60 zeros
• Practical millions of prints compared over 100
  years never found two the same

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RARITY

• Exceptional circumstances connected with the
  place, time or general conditions under which
  physical evidence is discovered can heighten its
  quality
• Example A hairpin found near murdered wonam may
  not be of as much value as a mans tie clasp

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CLASS CHARACTERISTICS

• Definition
• Properties of evidence that can only be
  associated with a group and never with a single
  source
• Disappointments when Lab unable to relate
  evidence to a common source with a high degree of
  probability

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CLASS CHARACTERISTICS

• Weakness
• Inability of examiner to assign exact or
  approximate probability values to the comparison
  of most pyhsical evidence
• Scientist attempt to creat or update statistical
  databases when possible
• Mostly forensic scientist must rely on personal
  experience to interpret significance of comparison

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CLASS CHARACTERISTICS

• Efforts made to find individual evidence
• Fingerprints, DNA, Firearms match
• Most physical evidence is class match
• Majority of evidence in case is subjetive
• Eye witness, confessions, informant
• Physical evidence provides corroboration

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CLASS CHARACTERISTICS

• Trying to find define the significance of class
  evidence in exact mathematical terms is difficult
  if not impossible
• Class evidence by definition is not unique
• Only objects that exhibit a significant amount of
  diversity are appropriate for physical evidence
• colored fibers v. white cotton

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CLASS CHARACTERISTICS

• Must provide evidence that would convince a
  reasonable man that there is no other explanation
• Dealing with more than one type of physical
  evidence, their collective presence leads to a
  high degree of certainty

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CLASS CHARACTERISTICS

• Must consider reality in courtroom
• Weight or significance left entirely to jury
• Lay people usually give scientist high degree of
  significance
• Scientific testimony takes on more reliability in
  courtroom
• Given great weight in deliberations

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PHYSICAL EVIDENCE

• When does class characteristic become individual
  characteristic
• Source of debate and disagreement
• EXAMPLES
• How many striations to match bullet
• How many paint layers to individualize
• How many ridges to match fingerprint

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PHYSICAL EVIDENCE

• Find as many characteristics as possible to
  compare substances
• Significance decided by
• Quality of evidence
• Composition of evidence
• Case history
• Examiners experience
• Conclusion can reach from speculation to near
  certainty

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PHYSICAL EVIDENCE

• Properties and characteristics
• Practical limits
• Extreme No two things are alike in every detail
• Modern analytical techniques have become too
  sensitive in some cases
• Learning how to use instruments part of work
• Proficiency to interpret findings critical

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PHYSICAL EVIDENCE

• CRIME SCENE RECONSTRUCTION

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CRIME SCENE RECONSTRUCTION

• Team event
• Reconstruct events that occurred
• Prior to crime
• During crime
• Subsequent to crime
• Collaborative effort including
• Law enforcement, criminalist, Medical examiners

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RECONSTRUCTION

• All professionals bring unique perspective
• Try to answer questions about crime
• How many people involved
• Cause of death
• Was there an attempt to cover up
• Physical evidence plays critical role in
  reconstructing events

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RECONSTRUCTION

• Physical evidence can
• Support accounts given by witnesses/suspects
• Contradict accounts given by witnesses/suspects
• Generate leads
• Confirm reconstruction to jury
• Physical evidence is the foundation of
  reconstruction

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RECONSTRUCTION

• Actions law enforcement must take to optimize
  reconstruction
• 1. Crime scene protection and security
• A continuous process (beginning to end)
• Evidence can be destroyed by walking through
• There is the possibility of contamination from
  persons allowed in the scene

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RECONSTRUCTION

• 2. Preliminary examination
• See scene as left by perpetrator
• Experience and physical evidence critical
• Captures nature of scene
• Hypothesize what happened
• Document observations
• Determine how scene should be worked

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RECONSTRUCTION

• 3. Involve other professionals
• Medical examiners
• Position of body
• Injuries
• Has body been moved
• Clothed before or after death
• Cause of death
• Estimate of time of death (not very accurate)

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RECONSTRUCTION

• 3. Other professionals
• Criminalists
• Approximate bullet path (lasers)
• Blood spatter analysis (chapter 12)
• Glass penetration (Chapter 4)
• Gunshot residue for distance (Chapter 15)

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RECONSTRUCTION

• From text
• Reconstruction supports a likely series of
  events by the observation and evaluation of
  physical evidence, as well as statements made by
  witnesses and those involved with the incident

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RECONSTRUCTION

• Team effort
• Put together different pieces of the puzzle
• Need right connections to show relationship
  between victim, suspect, and crime scene
• Can play a vital role in helping jury arrive at
  proper verdict

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