Crime-Scene Investigation and
Evidence Collection
Objectives
 Are there cars parked on the sides of the road?
 What color is the pickup truck driving in the
road?
 Any minivans around?
 What does the blue sign say?
 What’s the speed limit?
 Are there any pedestrians on the road?
Locard’s Exchange Principle
 When a person comes into contact with an object or another
person, a cross-transfer of physical evidence can occur
 Hair, skin cells, clothing fibers, pollen, glass fragments, debris from
clothing, makeup, soil
 Called trace evidence
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pet hair on clothes
Hair on your brush
Fingerprints on glass
Soil tracked into house
Drop of blood on t-shirt
Used tissue
Paint chips
Broken glass
Fiber from clothing
Evidence
 Classified two different ways –
 Direct evidence
 Circumstantial evidence
 Physical evidence
 Biological evidence
 Trace evidence
Direct Evidence
 Firsthand observations such as eyewitness accounts or police
dashboard video cameras
 Confessions
 Testimony by a witness in court
Circumstantial Evidence
 Indirect evidence that can be used to imply a fact but that
does not directly prove it
 Link between crime scene and a suspect
 Physical – Impressions, fingerprints, footprints, shoe prints,
tire impressions, tool marks, fibers, weapons, bullets, shell
casings
 Reduces number of suspects to a specific, smaller group
 Biological – body fluids, hair, plant parts, natural fibers
 Makes the group of suspects very small, or reduces it to a likely
individual
Class vs. Individual Evidence
 Class – narrows identity to a group of persons or things
 Ex – blood type
 Individual – narrows an identity to a single person or thing
 Ex – fingerprints
The CSI Team
 Police officers
 District attorney
 Crime scene investigators
 Medical examiners
 Detectives
 Specialists
The Crime Scene Investigation Team
 Police officers – secure the scene
 District attorney – determine whether search warrant is
necessary
 Crime-scene investigators – document crime scene in detail
and collect physical evidence
 Recorders, sketch artists, photographers, evidence collectors
 Medical examiners – determine cause of death if homicide
 Detectives – look for leads by interviewing witnesses and
talking to crime-scene investigators about evidence
 Specialists – consulted if the evidence requires their expertise
 Entomologists, forensic scientists, forensic psychologists, etc.
The Seven S’s of Crime Scene
Investigation
1.
Securing the scene
2. Separating the witnesses
3. Scanning the scene
4. Seeing the scene
5. Sketching the scene
6. Searching for evidence
7. Securing and collecting evidence
1. Securing the Scene
 Responsibility of the first responder (usually a police
officer)
 Restricts all persons not authorized from entering
 Security log of all entering and exiting
 May request various experts to be sent to scene
 First Priority – safety of all individuals
 Second Priority – preservation of evidence
2. Separating Witnesses
 Witnesses must not be allowed to talk to one another!
 Questions to ask:
 When did the crime occur?
 Who called in the crime?
 Who is the victim?
 Can the perpetrator be identified?
 Where were you when you observed the crime scene?
3. Scanning the Scene
 Scan the scene to determine where photos should be
taken
 Primary crime scene – where crime took place
 Secondary crime scene – location linking to crime
 Ex: Primary scene - front of store where robbery took
place
Secondary scene – home of suspect
Ex: Primary scene – location of murder
Secondary scene – location where corpse was found
4. Seeing the Scene
 Crime examiner needs to see whole scene
 NEEDS TO BE IN UNALTERED POSITION!!!
 Photos of overall area
 Close-up photos
 Photos with and without a measuring ruler
 View of crime scene from different angles and
distances
 Close-up photos of any evidence and bodies
 Photos need to be taken before evidence or body is
moved
360 view
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360 view
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5. Sketching the Scene
 Rough sketch – notes position of body and any other
evidence
 All objects measured from two immovable landmarks
 North should be labeled, scale included for distance
 Doors, windows, furniture
 If outdoors, position of trees, vehicles, hedges, other
structures
 Drawn AT the scene
 Also include – name, date, location, conditions
outside or inside
Figure 2–4 Rough-sketch
diagram of a crime scene.
Courtesy Sirchie Finger Print
Laboratories, Inc., Youngsville,
N.C., www.sirchie.com.
5. Sketching the Scene
 Final Sketch – include all the aspects of a rough sketch
but more accurate
 Possible for presentation in court
 Computer programs available now
 Drawn in the lab AFTER searching the crime scene
 Note-taking also occurs throughout entire process
Figure 2–5 Finishedsketch diagram of a
crime scene. Courtesy
Sirchie Finger Print
Laboratories, Inc.,
Youngsville, N.C.,
www.sirchie.com
6. Searching for evidence
 Scene should be walked and location of evidence marked,
photographed, and sketched
 Patterns:
 Spiral
 Grid
 Linear
 Quadrant or Zone
 Single investigator – grid, linear, or spiral pattern
 Group of investigators – linear, zone, quadrant
7. Securing and Collecting Evidence
 All must be properly packaged, sealed, and labeled
 Liquids and arson – stored in airtight, unbreakable
container
 Biological evidence – stored in breathable containers so
air can dry out
 Wet evidence – stored in paper and allowed to air dry
 NEVER place wet evidence in an airtight container; will cause
mold and degrade DNA
 Paper bindle – paper used to store evidence
 Placed into evidence bag and labeled
Standards
 There are many standards for collecting different
types of evidence
 Example: National Institute of Justice
Control Samples
 Obtained from the victim for the purpose of
exclusion
 Ex - blood samples found on a victim or at crime
scene compared to victim’s blood
 If they match, sample is victims and no further
tests run
 If not, may have come from suspect and further
testing is completed!
Evidence Log
 Case number
 Item inventory number
 Description of evidence
 Name of suspect
 Name of victim
 Date and time of recovery
 Signature of person recovering evidence
 Signature of any witnesses present during collection
Chain of Custody
 Each person who handles the evidence must be recorded
properly
When evidence is found – marked with proper information
and placed in a collection bag
2. Container is sealed and collector’s signature is written
across sealed edge
3. Next person responsible opens at a location other than
sealed edge, completes exam, reseals in new packaging and
signs chain of custody log!
4. Pattern continues!
1.
Chain of Custody
 EXTREMELY important for courtroom!
 All who handled evidence could be asked to appear in court
 Process must show evidence was handled properly and every
person handling it was recorded
Analyze the Evidence
 FBI crime lab is one of largest forensic labs in the world!
 Forensic Lab Technicians – specialized and process only
one type of evidence
 Lead detective – lab results sent to him
 Looks at evidence and attempts to determine how it fits into
overall crime scenario
 Must consider all possible interpretations for evidence
Use of Evidence
 Evidence compared to witness’ statements
 Can link a suspect to scene or a victim
 Establish the identity of a victim
 Confirm verbal witness testimony
 Acquit the innocent
Crime Scene Reconstruction
 Forms a hypothesis of the sequence of events from
before the crime was committed through its commission
 Evidence does not lie, but could be staged!
 Evidence is used to determine overall crime scenario
Crime Scene Safety
 The increasing spread of AIDS and hepatitis B has
sensitized the law enforcement community to the
potential health hazards that can exist at crime scenes.
 In reality, law enforcement officers have an extremely
small chance of contracting AIDS or hepatitis at the
crime scene.
 The International Association for Identification Safety
Committee has proposed guidelines to protect
investigators at crime scenes containing potentially
infectious materials that should be adhered to at all
times.
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Crime Scene Safety
1.
2.
3.
4.
At crime scenes where blood or body fluids involved:
latex gloves and shoe coverings should be warn.
If potentially infectious dust or mist encountered:
particle mask/ respirator, goggles, or face shield
recommended also.
Personnel should be aware of sharp objects, knives,
hypodermic syringes, razor blades, etc and place them
in appropriate container with label.
Red biohazard bag should be used for disposal of
contaminated gloves, clothing, masks, pencils, etc. and
removal to approved biohazardous waste pickup.
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Crime Scene Safety
5. Note-taking should be done while wearing
uncontaminated gloves to avoid contamination or
pens, pencils, notebook, paper, etc.
6. If personal protective equipment (PPE) becomes torn, must
be removed immediately and person must decontaminate the
potentially contaminated body area with recommended
solution.
7.
No eating, drinking, smoking, or applying makeup at scene of a
crime.
8.
All nondisposable items (lab coats, towels, personal clothing)
that may be contaminated are placed in a yellow plastic bag,
labeled “Infectious Linen” and laundered by a qualified service.
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