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Processing the crime scene


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  • 1. Processing the Crime Scene Securing Physical Evidence
  • 2. What is Physical Evidence? Any and all objects that can:  establish that a crime has been committed  link a crime and a victim  link a crime and the perpetrator Selectivity is the key  You can’t collect everything!
  • 3. Priorities at the Crime Scene Obtain medical aid for those in need Arrest the perpetrator Secure the crime scene  Exclude unauthorized personnel  Remember Locard’s Exchange Principle!  Determine crime scene boundaries  Locate path of entry and exit
  • 4. Photography Scene must be unaltered!  If objects are removed, positions changed, or items added photos may be inadmissable  If items were moved (eg. Securing a firearm) note it in the report, do not put it back! Physical evidence must be photographed to show:  Position and location relative to the scene  Close-ups to show detail  Scale to show size
  • 5. Sketches Rough sketch records  Dimensions of crime scene and surroundings  Location of each piece of physical evidence  Distances from two points Finished sketch  Represents crime scene to the jury
  • 6. Systematic Search Patterns Spiral search Grid method Strip of line search Quadrant or zone search
  • 7. Evidence Collection Must collect all possible carriers of evidence  Clothing  Package each item separately  Cross- contamination  Sweepings  Collect and package each area separately  Fingernail scrapings
  • 8. Evidence Collection Must collect all possible carriers of evidence  Head and pubic hairs  For comparison purposes  Blood or cheek swab for DNA  Vaginal, anal and oral swabs  For sex crimes  Recovered bullets from the body  Hand swabs for gunshot residue
  • 9. Special Considerations for Arson Accelerants  Volatile, evaporate easily  Collect ash and debris for traces  Store in airtight paint cans with vapor concentrators
  • 10. Standard/Reference Samples To show provenance  Substrate Controls you need known  Samples of materials reference samples to near where physical compare to evidence was  Hair deposited  Fiber  Want to show tests for physical evidence  Glass don’t produce false  DNA positives  Blood  Untouched wallboard in arson  Background fabric for blood test
  • 11. Chain of Custody Key point of attack for the defense Every person who handled or examined the evidence must be accounted for  Must be a written record of each hand- off  Each time container is opened a fresh seal must be made and initialed
  • 12. Safety Considerations AIDS and other infectious materials  Double gloves, shoe covers, Tyvek suit  Blood must be dried  Biohazard bags Air-borne particulates and dust  Particle mask, respirator, goggles, face shield Sharps and blood contamination No eating, drinking, smoking, putting on make-up
  • 13. Legal Considerations 4th Amendment Rights  Right against unreasonable search and seizure  Probable cause  Description of place to be searched  Description of persons or things to be seized
  • 14. Searching without a warrant Emergency circumstances Prevent loss or destruction of evidence Search of person and property during an arrest Search made with consent
  • 15. Key Court Decisions Mincey v. Arizona  Undercover cop killed trying to buy drugs  Police search scene for four days without obtaining a warrant  Supreme Court throws out the evidence found  “No exigent circumstances”
  • 16. Key Court Decisions Michigan v. Tyler  Arson at a place of business  Police search scene looking for arson but leave scene unattended for several hours  Return several times over next 4 weeks to collect evidence without warrant  Initial warrantless search is OK after fire  Later searches thrown out