UNIT OVERVIEW
• Processing a Crime Scene
• Evidence Team
• Crime Scene Searches
• Evidence Collection and
Packaging
• Chain of Custody
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Legal Precedent
Physical Evidence
Locard’s Exchange Principle
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Every contact leaves a trace!
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Whenever two objects come together they must
affect each other in some way. Something is likely to
be exchanged between them!
Physical Evidence encompasses any and all objects
that can establish that a crime has
been committed or can provide a
link between a crime and its victim
or a crime and its perpetrator
Secure and Isolate the Crime Scene
•1st officer:
•preserve and protect the area to greatest
extent
•Obtain medical attention
•Preserve and protect evidence (isolate area)
•Exclude unauthorized personnel (Every
individual who enters is potential destroyer of evidence)
•Designate Officer in Charge
•Establish boundaries
•Document site/Evaluate area
•Collection of evidence
Crime Scene Team
A group of professionals trained in a
variety of special disciplines
Evidence Team members
 First police officer on the scene
(Team Leader)
 Medics (if necessary)
 Photographer and Notetaker
 Sketch team
 Evidence Recovery Personnel
 Lab experts/specialists
First Officer on the Scene - Team Leader
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Assume control and access
scene
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Determine search pattern and
assignments
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Coordinate with groups
involved
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Continuously evaluate work
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Release Crime Scene
Crime Scene Survey
Walk-through—performed by the crime scene
investigator, the first officer, and
sometimes the lead detective
Purpose:
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Mentally prepare a reconstruction theory
Note any conditional evidence that could change over time
Note environmental and weather conditions
Note points of entry or exit, as well as paths of travel within the
crime scene
Record initial observations of who, what, where, when, and how
Identify special needs within the crime scene for personnel,
precautions, or equipment and notify superior officers or
other agencies
Recording the Scene
Permanently record crime scene so original
state is not lost
 Documentation is required for presentation at
trial
 Photography
 Sketches
 Notes
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Documenting the Scene
Taking Notes
Must include detailed written description
of scene with enough detail to refresh
memory months later
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date, time, description of the location
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weather and environmental conditions
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description of the crime
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location of the evidence relative to
other key points
the names of all people involved
modifications that have occurred and
other relevant information
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Documenting the Scene
Photography
 photos of entire scene and surroundings (overlap by 30%)
 mid-range to close-up photos with various angles of each piece of evidence
 Photograph evidence before it’s moved (including fingerprints, casts, etc.)
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Photograph evidence both in wide view (position at scene) and close-up
(with scale)
 Photos as viewed by any witnesses
 All photos logged
Videography
 allows for narration (non-subjective) and
different perspectives but does NOT
replace still photos
Capture Crime Scene
Wide angle lenses are used to distort the truth
or emphasis it
Details preserved
Proper Technique
(Courtesy of Phil Orlando)
38 Caliber and 44 Caliber
Documenting the Scene
Sketches (Rough and
Finished)
 Inclusion of date, time, scale
 Reference points and distance
measurements
 Names of investigators, victims,
suspects
 A legend (key)
Finished Sketch
•Can be hand drawn or computer
generated
•Drawn to scale
•Aesthetic appearance
Crime Scene Searches
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Must be thorough and systematic
Thorough search for evidence must be conducted
immediately
How investigation carried out depends on locale, size of
area, actions of suspects & victim(s) at scene.
Steps:
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One person supervises or coordinates
collection of evidence
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Scene subdivided into segments
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Search may be geared outward or
inward
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Areas searched must include all
possible points of entry and exit
Methods of Searching a Crime Scene
Line or strip method
 Best in large, outdoor scenes
 Need many people to be most effective
 Must move slow and
cover the area multiple
times
Grid Search
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Basically a double-line search
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Effective, but timeconsuming
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Can be done with fewer
people
Zone or quadrant
method
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Most effective in houses, buildings,
or large areas
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Teams are assigned zones for
searching
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Usually based on floor plans or
land areas
Spiral method
 Best on small, circular crime scenes
 May move inward or outward
 Best used where there are no/limited physical barriers
Evidence Recovery Personnel
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Describe evidence and location on container
Package evidence separately
Maintain chain of custody and evidence log
Ensure proper safety of collection (e.g., infectious
materials)
What to think about?
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Who did it?
What happened?
When did it happen?
How did it happen?
Did it happen here or was another crime scene involved?
Who is the victim?
Why was this crime committed?
What evidence is there to help prove the motive and the
crime?
Physical Evidence Includes
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Anything from massive objects to microscopic traces
Evidence may be obvious, but some can only be
detected through examination in the crime lab
Examples:
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Victims clothing
Fingernail scrapings
Head and pubic hairs
Blood (for DNA typing purposes)
Vaginal, anal and oral swabs (in sex related)
Recovered bullets from the body
Hand swabs from shooting victims (for gunshot residue analysis)
Collecting & Packaging Evidence
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The most fragile evidence is
collected and packaged first.
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Different types of evidence
require specific or special
collection and packaging
techniques.
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The type of container depends
on sample
(nothing wet in sealed plastic)
Changes can occur through:
Contamination
Breakage
Evaporation
Accidental scratching or bending
Loss through improper or careless
packaging
Types of Packaging
Many items are packaged in a primary
container and then a secondary one.
Pill bottles, vials, manila envelopes, and plastic
bags are good for most evidence.
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 Trace
evidence may be placed on a piece of
paper which is then folded in a particular way
called a “druggist’s fold.”
Secondary containers such as paper bags,
plastic bags, canisters, packets, or envelopes are
used depending on the type and size of the
evidence.
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How to maintain integrity of evidence
Item kept in original condition as found
 Submit intact
 Blood, hairs, fibers, soil particles, etc should not be
removed from garments, weapons or other items that
bear them (send entire object for testing)
 Removal from large object (wall) using forceps and
packaging
 Bloodstains: scraping, transferring to a moistened swab,
cut out area of object bearing stain
 Biological evidence such as dried blood should be
packaged in paper ~ Liquid blood can be collected in a
glass tube but SHOULD NOT be frozen
 Packages should be sealed and marked with your initials
and date collected
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ALL handlers are responsible for the integrity the evidence
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Chain of Custody: There must be a written
record of all those who have had possession of
an item of evidence, beginning at the time of
collection (The first person who comes in contact with that evidence
should fill out a chain of custody tag.)
 The evidence container must be marked for
identification.
 The collector’s initials placed on the seal.
 If evidence is turned over to another person, the
transfer must be recorded.
Evidence submission to Laboratory
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Evidence submission forms must accompany all
evidence
Brief history of case
Type of examinations requested
List of items submitted for examination
Obtain Standards/Reference Samples and Controls
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Examination of evidence requires a comparison with a control for
verification
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Quality & quantity of reference samples lends weight to their value
Safety Guidelines from the International
Association for Identification Safety
Committee
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Personnel wear a minimum of latex gloves (double gloved) and
protective (Tyvek-type) shoe covers.
Use of masks/respirators, goggles or face shields
Be alert to sharp objects (knives, hypodermic needles, razor
blades…)
Maintain a red biohazard plastic bag for disposal of potential
infectious materials
Note taking done with non-contaminated gloves
Soiled/torn protective equipment should be removed immediately
and disinfected using recommended solutions (10% bleach)
No eating or drinking aat the crime scene
Personal clothing that may have been contaminated should never
be taken home
Legal Considerations at the Crime Scene
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“Unreasonable search and seizure”
removal of evidence must conform to 4th
amendment:
“The right of the people to be secure in their persons, houses,
papers and effects against unreasonable searches and seizure, shall
not be violated, and no warrants shall issue, but upon probable
cause, supported by oath or affirmation, and particularly describing
the place to be searched and the persons or things to be seized.”
Allowances for Warrantless searches
 The existence of an emergency.
 The need to prevent the immediate destruction of
evidence.
 In plain view
 A search of a person or property within the
immediate control of the person provided it is made
incident to a lawful arrest.
 A search made by consent of the person involved.
Legal Precedent
MINCEY v. ARIZONA (U.S. Supreme Court, 1978)
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Drug bust that went wrong and an undercover police
officer was killed.
Police spent 4 days searching and seizing evidence
Mincey arrested and convicted.
Supreme Court ruled evidence collected was
inadmissible because it was not from a proper search
and seizure.
Evidence taken without proper authority is
probably not legally admissible
Michigan v. Tyler (U.S. Supreme Court, 1978)
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Building destroyed by fire was put out in early AM.
Building left unsecured until 8 AM when a preliminary
search was done (for cause of fire).
Subsequent searches (at 4, 7, and 25 days) removed
additional evidence.
Tyler convicted of arson.
However….Supreme Court overturned conviction.
◦ “…entry to fight a fire requires no warrant, and that
once in the building, officials may remain there for a
reasonable time to investigate the cause of the blaze.
Thereafter, additional entries to investigate the cause of
the fire must be made pursuant to the warrant
procedures”