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