Unit AC rime Scene Processing

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Unit AC rime Scene Processing Powered By Docstoc
					  Forensic Science:
   An Introduction
Unit A: Crime Scene Processing
 Forensic Science - the application of the
  knowledge and technology of science to
  the criminal and civil laws that are
  enforced by police agencies in a criminal
  justice system.
 Locard’s Exchange Principle – when two
  objects come in contact with each other, a
  cross-transfer of materials occur. This
  allows us to connect criminals to crime
       The American Academy of
     Forensic Science Departments
   Criminalistics - crime scene processing
   Engineering Science - reconstruction
   General
   Jurisprudence - legal
   Odontology - bitemarks
   Pathology/Biology – autopsy, DNA
   Physical Anthropology – skeletal remains
   Psychiatry and Behavioral Science
   Questioned Documents
   Toxicology – drugs and poisons
       Additional disciplines
 Fingerprint examination
 Firearm and toolmark examination
 Computer and digital analysis
 Photography
 Entomology - insects
          Historical Events
 Late 1700s - Arsenic and Toxicology
 Mid 1800s – Microscopy
 Late 1800s – Identification (Bertillion)
 Early 1900s – Fingerprinting, Blood and
  Serology, Document Examination,
 Mid 1900s – Chromatography,
  Spectrophotometry, Electrophoresis, DNA
   Yi Yu Ji “A Collection of Criminal Cases”
   “A Treatise on Forensic Medicine and Public
    Health” (Fodere, 1798)
   “Finger Prints” (Galton, 1892)
   “Criminal Investigation” (Gross, 1893)
   Sherlock Holmes –fiction (Doyle 1880s)
   “Treaty of Criminalistics (Locard, 1931)
   Hypervariable Minisatellite Regions in Human
    DNA (Jeffreys, 1985)
                Crime Labs
   Locard
   Los Angeles - oldest
   FBI
   DEA
   ATF
   US Postal Service
   SBI
   State system
   Local
   Delocalized labs – no common management
        Crime Lab Services
Basic Services       Optional Services
 Photography         Toxicology
 Physical Science    Latent Fingerprint
 Biology/DNA         Polygraphy
 Firearms            Voice Analysis
 Document              Forensic Psychiatry
                        Forensic Odontology
                        Forensic Engineering
                        Forensic Computer
                         and Digital Analysis
    What Forensic Scientists Do
   Analyze physical evidence
       Use scientific methods
   Determine admissibility of evidence
       Frye v US (1923) – general acceptance
   Judge scientific evidence
       Daubert case (1993) – trial judge is gatekeeper
 Provide expert testimony
 Furnish training
            Forensic Science
 Forensic scientist seek to reach truth
  based on available evidence. The legal
  process does not, however, always seek
  truth but follow process.
 Reliable methods possess characteristics
     Integrity
     Competence
     Defensible technique
     Relevant experience
          Reliable Methods
 Help distinguish evidence from
 Allow alternative results to be ranked by
  basic scientific principles
 Allow tests to either prove or disprove
  alternative hypotheses
 Pursue testing by breaking hypotheses
  into their smallest logical components
          Physical Evidence
 Anything physical objects that can link a
  crime to its victims or to suspects.
 Has to be collected from crime scene
 Must be relevant to the crime
 Requires the collector to understand what
  the capabilities and limitations of the crime
  lab are
         Physical Evidence
 Crime labs do not solve crimes, only add
  evidence to help police investigation link
  the suspect to the crime.
 The forensic scientists must know how to
  collect and preserve evidence found at the
  crime scene
 Ways to classify a crime scene
 Primary vs secondary crime scene
 Macroscopic vs microscopic scenes
 Type of crime
 Location of crime
    Use of Physical Evidence
 Information on evidence of a crime
  (Corpus Delecti)
 Information on the criminal (Modus
 Linkage on persons, scenes and objects
 Identification of suspects
 Identification of unknown substances
 Reconstruction of a crime
 Providing investigative leads
    Arriving at the Crime Scene
 Secure and isolate the crime scene
 Determine boundaries of crime scene and
  priorities for evidence collection
 Rough sketch
 Finished sketch
 Photograph
 Videotaping
 Notes
        Collecting Evidence
 Conduct a systematic search for evidence;
  be unabiased and thorough.
 Field technicians
 What to look for depends on the crime and
  what specific locations of the crime scene
  would most likely be affected
 Microscopic or massive objects
 Collect carriers of possible evidence
 Vacuum or sweeping collected
       Packaging of Evidence
 Prevent any changes from occurring
  (contamination, breakage, evaporation,
  bending, loss)
 Process trace evidence from original
  object (shirt, shoe) rather than isolating
  and packaging if possible
 Package evidence separately
    Tools for Collecting Evidence
 Forceps
 Evidence envelopes and pill bottles
 Swabs
 Special concerns (mold, evaporation)
 Various light sources
 Latent fingerprints
 Mobile crime labs or better yet crime
  scene search vehicle
           Chain of custody

 Continuity of possession; every person
  who touched it must be accounted for
 Standards for collecting, labeling, and
  submitting evidence forms are necessary
  for court
 Labels include collectors initials, location
  of evidence, date of collection.
  Identification numbers must also be used
     Submission of Evidence
 Standard/reference samples
 Substance controls
 Evidence submission form will detail the
  evidence collect and particular type of
  examination/analysis requested.
 Lab tech not bound by requests
     Common Types of Evidence
   Common Types of               Paint
    Evidence                      Petroleum products
   Blood, semen, and saliva      Plastic bags
   Documents                     Plastic, rubber, and other
   Drugs                          polymers
   Fibers                        Powder residues
   Fingerprints                  Serial numbers
   Firearms and ammunition       Soil and minerals
   Glass                         Tool marks
   Hair                          Vehicle lights
   Impressions                   Wood and other
   Organs and physiological       vegetative matter
Examination of Physical Evidence
   Identification
       Determining the identity of a substance with a near
        absolute certainty while ruling out other substances
   Comparison
       Comparing the evidence to one or more selected
        references and drawing a conclusion about its origins.
       Individual characteristics –properties of evidence that
        can be attributed to a common source with extremely
        high certainty. (eg. fingerprints, DNA, bullets)
       Class characteristics – properties of evidence that
        can be associated with a group and never with a
        single source. ( eg. Blood type, tire marks)
    Significance of Physical Evidence
   Assessing the values of evidence
       Class characteristics of evidence is valuable in
        corroborating events.
       Multiple class evidence can lead to a high level of
        certainty of origin
   Cautions and limitations of evidence
    A person can be exonerated or excluded from
    suspicion if evidence collected from the crime
    scene is different from the reference samples
    collected from the person.
           Forensic Databases
   One-on-one comparison requires a suspect
   Computerized databases help link evidence to
   Fingerprint databases – IAFIS
   DNA database – CoDIS
   Ballistics database – IBIS
   Automative Paint database – PDQ
   Shoeprint database - SICaR
    Crime-Scene Reconstruction

 The method used to support a likely
  sequence of events at a crime scene by
  observing and evaluating physical
  evidence and statements made by those
  involved with the incident
 Combined efforts of MEs, CSI, and law
  enforcement personnel
 Examples: was body moved, bullet
  trajectory, blood splatter
   Alphonse Bertillion (1883) – anthropometry
   Henry Fauld (1880) - first published on possible
    use of fingerprints
   Francis Galton (1892) – published Finger Prints
    described types of prints
   Sir Edward Henry (1897) – classification system
    used today
   FBI (1924) – new formed FBI held world’s
    largest fingerprint database
              Fingerprint Principles
   1. A fingerprint is an individual characteristic; no two
    fingerprints have been found to possess identical ridge
       No minimum number of comparisons to establish identity
   2. A fingerprint remains unchanged during an individual’s
       Friction ridges and grooves created by dermal papillae
       Sweat glands on the ridges deposit perspiration and oils
       Latent fingerprint – left by deposits and is invisible to the naked
   3. Fingerprints have general ridge patterns that permit
    them to be systematically classified.
        Categories of Fingerprints
   Loop – ridge lines enter one side of
    pattern and curve around to exit from the
    same side of pattern. (65%)
     Ulnar loop – opens toward little finger
     Radial loop – opens toward thumb

         Ulnar Loop       Radial Loop
        Categories of Fingerprints
   Whorl – ridge lines rounded or circular and
    have two deltas(30-35%)
       Plain whorl

       Central pocket loop

       Double loop

       Accidental loop
        Categories of Fingerprints
   Arch – ridge lines enter print from one side
    and exit from the other (5%)
       Plain

       Tented
     Classification of Fingerprints
   Henry system – numerical system involving the
    presence or absence of the whorl pattern on
    each finger as part of the primary classification..
       This does not identify someone, only reduce the
        number of possible candidates
   AFIS – 10 print system that can search 500,000
    stored ten-prints in 0.8 seconds
       Data entered now by Livescan rather than ink rolling.
       Human decisions must still be made
       Software incompatibilities among states
          Methods of Detection
   Types of prints
     Latent print
     Visible print – deposited ink, blood, dirt
     Plastic print – impression in a soft surface

   Locating prints – RUVIS
             Developing Prints
   Powders
     Charcoal
     Magnetic
     Fluorescent

   Chemicals
     Iodine fuming (sublimation)
     Ninhydrin
     Physical developer (silver nitrate)
     Super Glue fuming
     Alternate Light Sources/ LED
    Preservation of Developed
 Photographs
 Print surface should be removed in its
  entirety (covered with cellophane)
 Lifted from surface with tape
 Digital imaging into pixels – allows
  adjustments to be made to enhance

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