1. Processing the Crime Scene
Securing
Physical
Evidence
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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
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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