Introduction to Crime Scene Investigation - PowerPoint by WqO2CZ6


									Introduction to Crime Scene
       Thanks to Edward E. Hueske
        University of North Texas
             Denton, Texas
    Duties of First Officer to Scene
•   Make scene safe for entry
•   Provide medical attention to injured
•   Secure scene
•   Preserve physical evidence
•   Detain witnesses
•   Request assistance as needed
       Crime Scene Investigation
•   Team approach will be used
•   One person must be in charge
•   Equipment and supplies must be present
•   Duties must be designated
•   Search method(s) must be established
•   Security of scene must be confirmed
•   Priorities in processing must be established
           The Team Approach
• Team leader is established prior to arrival

                           Thanks a lot

   This one’s yours,
   I had the last one
          Duties of Team Leader
•   Meet with first officer for briefing
•   Confirm security
•   Determine legality of search (search warrant)
•   Call for additional personnel/equipment
•   Survey scene with first officer
•   Note fragile evidence/establish priorities
•   Make notes as to initial observations
•   Work out action plan with team
    Appropriate Crime Scene Attire
•   Gloves
•   Shoe covers
•   Disposable suit
•   Head gear
•   Eye protection
•   Breathing apparatus
     Appropriate Crime Scene
• Do not smoke, eat, drink, etc. within the
• Do not bring equipment into scene and set
  down within the scene if at all possible
• Do not place foreign items down in scene
        Documenting the Scene
•   Photography
•   Video Taping
•   Sketching
•   Diagramming
•   Note Taking
•   Report Writing
              Scene Searches

•   Spiral search
•   Line (strip) search
•   Grid search
•   Quadrant (sector)
            Vehicle Searches
•   Photograph as found
•   Begin with exterior exam/print search
•   Divide interior into areas
•   Undercarriage exam (hit & runs)
•   Inventory and document items as removed
•   Have items tested as appropriate
            Autopsy Evidence
•   Hair standards
•   Blood samples – purple-topped tubes
•   Prints
•   Fingernail scrapings
•   GSR test
•   Sexual assault kit
•   Recovered bullets, etc.
    Collection and Packaging of
• Do not use plastic to package biological evidence
• Most evidence is best packaged by placing into a
  clean sheet of paper, folding, taping and placing in
  an envelope and sealing
• Package evidence separately
• Use sharps containers when needed
• Obtain required control samples
• Maintain a chain of custody record
• Use biohazard bag to dispose of contaminated
  items (gloves, shoe covers, etc.)
     Crime Scene Photography
         •   First frame is data card (ea. Roll)
         •   General to specific
         •   Outside to inside
         •   Special documentation (street sign,
             house number, VIN tag, etc.)

Remember: You can’t take too many pictures, but you can
take too few!
       Crime Scene Photography
                Scaled Photography

•   Camera back is in same plane as subject
•   Fill frame with subject
•   Include a scale in 1 photo & 1 w/o scale
•   Use oblique lighting as required
•   Use a tripod and remote shutter release
Crime Scene Photography
        Specialized Techniques

•   Painting with light
•   Fill-flash
•   Spray paint “shadowing”
•   Luminol
     Crime Scene Photography
                 Painting with Light

• Use for night photography of large outdoor
• Use for time exposures of impressions in
  dust with flashlight
     Crime Scene Photography

• Use to show background with luminal
• Initial exposure of luminal reaction with
  lens wide open
• Manually fire strobe after exposure (use
  shield on strobe)
       Crime Scene Photography
               Spray Paint “Shadowing”

•   Use with available light
•   Use for impressions in snow
•   Use for impressions in sand or other soil
•   Flat black or flat white works best
•   Spray at an oblique angle
     Types of Physical Evidence
•   Blood, Semen and Saliva
•   Documents
•   Drugs
•   Explosives
•   Fibers
•   Fingerprints
•   Firearms evidence
    Types of Physical Evidence
• Glass
• Hair
• Two-dimensional and three-dimensional
• Body fluids and organs
• Paint
• Petroleum products
• Plastic bags (garbage)
     Types of Physical Evidence
•   Polymers & Plastics
•   Gunpowder Residues
•   Serial Numbers
•   Soil and Minerals
•   Tool Marks
•   Vehicle Lamp Bulbs
•   Wood & Vegetative Matter
  The Goal of Physical Evidence
• Positive Identification
• Association
• Circumstantial
     Comparative Analysis
• Known to Unknown or “Q” to “K”
• Physical comparison (physical
  properties/jig-saw puzzle fit)
• Chemical comparison
• Class characteristics
• Individual characteristics
         Range of Conclusions
•   Identification (common origin)
•   Same source or a similar source (either/or)
•   Member of same class (cannot be excluded)
•   Exclusion (different origin)
           Ignorance is Bliss

• What is a class characteristic?
• What is and individual characteristic?

          Knowledge is the key
     Evidence and Probability
• Most of the time a mathematical expression
  is inappropriate (Highly probable vs. highly
• Some situations do lend themselves to a
  mathematical expression of probability
  (DNA is a prime example)
       Probability and Statistics
• Coin toss – 1 in 2 probability
• Roll of a die – 1 in 6 probability
• Roll of a pair of dice to yield “snake eyes” – 1/6 x
  1/6 = 1/36 (1 in 36 probability)
• There are 4 aces in a deck of 52 cards, what is the
  probability of drawing an ace at random?
• What is the probability of drawing a king of any
• What is the probability of drawing an ace and a
  king with 2 draws from a full deck?
      Probability and Statistics
• DNA analysis is based on the presence of
  certain fragments within the DNA molecule
• For each fragment there is a certain
  frequency (probability of occurrence) within
  a particular ethnic group of a population
• If 7 different fragments are identified as
  being present, how is the probability of that
  occurring in someone else calculated?
      Probability and Statistics
• A vehicle with 4 different brands of tires
  leaves all 4 different tread patterns at a
  crime scene. A suspect is arrested with a
  car with 4 different tires, each similar to one
  of the crime scene impressions.
• Is it possible to calculate the probability of
  finding the same situation on another car?
• What considerations are involved?
           Negative Evidence
• “Absence of Evidence is not evidence of absence”
• Nevertheless, what is not present can provide
  useful information as to how a crime may have
  been committed
• Ex: No shoe impressions on driver side of vehicle
  but shoe impressions leaving the passenger side
• Faulty reasoning: no blood in trunk, therefore
  victim was not transported in trunk.
     Crime Scene Reconstruction
•   Who?
•   What?
•   When?
•   Where?
•   How?
•   Why?
     Crime Scene Reconstruction
•   On-scene
•   Off-scene
•   Re-enactment:
•   Live actors
•   Mannequins

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