Transcript Introduction to Crime Scene Investigation

Introduction to Crime Scene
Investigation
University of North Texas
Denton, Texas
Duties of First Officer to Scene
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Make scene safe for entry
Provide medical attention to injured
Secure scene
Preserve physical evidence
Detain witnesses
Request assistance as needed
Crime Scene Investigation
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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
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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
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Gloves
Shoe covers
Disposable suit
Head gear
Eye protection
Breathing apparatus
Appropriate Crime Scene
Behavior
• Do not smoke, eat, drink, etc. within the
scene
• 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
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Photography
Video Taping
Sketching
Diagramming
Note Taking
Report Writing
Scene Searches
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Spiral search
Line (strip) search
Grid search
Quadrant (sector)
Vehicle Searches
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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
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Hair standards
Blood samples – purple-topped tubes
Prints
Fingernail scrapings
GSR test
Sexual assault kit
Recovered bullets, etc.
Collection and Packaging of
Evidence
• 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
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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
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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
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Painting with light
Fill-flash
Spray paint “shadowing”
Luminol
Crime Scene Photography
Painting with Light
• Use for night photography of large outdoor
scenes
• Use for time exposures of impressions in
dust with flashlight
Crime Scene Photography
Fill-Flash
• 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”
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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
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Blood, Semen and Saliva
Documents
Drugs
Explosives
Fibers
Fingerprints
Firearms evidence
Types of Physical Evidence
• Glass
• Hair
• Two-dimensional and three-dimensional
Impressions
• Body fluids and organs
• Paint
• Petroleum products
• Plastic bags (garbage)
Types of Physical Evidence
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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
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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
improbable)
• 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
suit?
• 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
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Who?
What?
When?
Where?
How?
Why?
Crime Scene Reconstruction
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On-scene
Off-scene
Re-enactment:
Live actors
Mannequins