Crime Scene Investigation and Evidence Collection Lecture - PowerPoint PPT Presentation


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Crime Scene Investigation and Evidence Collection Lecture


Crime Scene Investigation and Evidence Collection Lecture Credits: Anthony (Bud) Bertino Goal to recognize, document and collect evidence at a crime scene – PowerPoint PPT presentation

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Title: Crime Scene Investigation and Evidence Collection Lecture

Crime Scene Investigation and Evidence Collection
Credits Anthony (Bud) Bertino
  • Goal to recognize, document and collect evidence
    at a crime scene

Locards Principle
  • Principle of Exchange
  • Part 1 when a person comes into contact with an
    object or another person, a cross transfer of
    physical evidence can occur

Part 2 the intensity, duration and nature of
materials in contact determine the extent of
  • leading to trace evidence on the individuals and
  • cross exchange bears as a silent witness
  • identified an attacker based on trace evidence
    underneath victims fingernail

Types of Evidence
Circumstantial indirect evidence
- used to imply but prove a fact - may link a
suspect and a crime scene ex. Suspects gun found
at crime scene
  • firsthand observations
  • eyewitness accounts
  • dashboard video cameras
  • confessions

Physical Impressions, Fibers, weapons,
bullets, shell casings reduces number of suspects
to group
Biological may make group of suspects very
small or even one individual Body fluids, hair,
plant parts, natural fibers
Individual evidence single person, DNA,
fingerprint, combination of unique traits
Class evidence narrows the identity to a group
ex. Blood type ABO
Trace evidence
  • Pet hair on clothes or rugs
  • Hair on brush
  • Fingerprints on glass
  • Soil tracked inside on shoes
  • Drop of blood on t shirt
  • A used facial tissue
  • Paint chips
  • Broken glass
  • Fiber from clothing

Crime Scene Investigation Team
  • Police Officers usually first (possibly a DA for
    a search warrant)
  • Crime Scene Investigators document crime and
    collect physical evidence
  • Recorder
  • Sketch artist
  • Photographers
  • Evidence collectors
  • Medical Examiners coroners may be necessary to
    determine cause of death in a homicide case
  • Detectives look for leads, interview witnesses
    and talking to the CSI about evidence
  • Specialists entomologists, psychologists

7 Ss of CSI
  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 the Evidence

Securing the Scene
  • First responding officers job
  • 1 SAFETY
  • 2 Preserve evidence
  • Protect area
  • Limit exchange
  • Request team

Separating the Witnesses
  • 3rd priority try to prevent collusion
  • Ask the following questions
  • When did the crime occur?
  • Who called in the crime?
  • Who is the victim?
  • Can the perpetrator be identified?
  • What did you see happen?
  • Where were you when you observed the crime scene?

  • Scan the scene to determine what photos are
  • May determine primary and secondary crime scene

Seeing the Scene
  • Photos of overall area
  • Close up photos with and without rulers
  • Triangulation of stationary objects should be
    included in the photos as reference point
  • View needs to be taken from several different
    angles and distances
  • Several close up photos of evidence and bodies

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accurate rough sketch is made noting position of
body if applicable and any other evidence All
objects should be measured from 2 immovable
landmarks Label N on the sketch and a scale Any
objects within the vicinity of crime scene
windows, furniture, doors. Outside position of
trees, vehicles, shrubs. Make another final
sketch for court
Sketching the Scene
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Searching for Evidence
  • Depends on number of investigators
  • Walk the scene marking location of evidence,
    photo, sketch
  • Single investigator use grid, linear or spiral
  • Group linear, zone or quadrant pattern
  • Patterns are systematic to ensure no area is left
  • Additional light for hair / fibers
  • Vacuum cleaner
  • Flashlight and forceps reduce picking up

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Securing and Collecting the Evidence
  • Must be properly packaged, sealed and labeled
  • Specific procedures must be followed for
    collection and storage
  • Liquids and arson remains airtight, unbreakable
  • Biological evidence breathable containers to
    reduce mold

After evidence is allowed to dry then packaged
into a paper bindle Paper bindle (druggist fold)
then placed in paper or plastic container Outer
container then sealed with tape and signed by the
collector on the label
Evidence log and Chain of Custody document in
attached to the evidence container.
  • Contains
  • Case number
  • Item inventory number
  • Description of the evidence
  • Name of the suspect
  • Name of the victim
  • Date and Time of recovery
  • Signature of person recovering evidence
  • Signature of any witnesses present during

CHAIN OF CUSTODY Must be maintained to secure
  • Collector finds evidence and bags it in paper or
  • The final container is the collection bag labeled
    with pertinent info
  • Seal and collectors signature written across
    sealed edge
  • Taken to a lab and signed over to technician
  • Tech opens bag (tears) somewhere not the sealed
  • Technician handles evidence then repackages
    evidence in original packaging and then seals in
    new packaging
  • Sign chain of custody log
  • Ensures responsible handling from crime scene to

Analyze Evidence
  • FBI crime is largest forensics lab in the world
  • Process all evidence to determine facts of the
  • Each technician has one specialty (one type of
  • Lab results sent to lead detective
  • Test results lead to crime scene reconstruction
  • hypothesis about sequence of events before
    crime to commission
  • Detective takes evidence and tries fit into
  • Analysis can link a suspect to scene or victim or
    lead to acquittal
  • Direct evidence is more compelling than

Crime Scene Reconstruction
  • Hypothetical sequence of events
  • Exam evidence and compare to witness accounts to
    determine reliability
  • Evidence does not lie but it can be staged

Staged Crime Scenes
  • Unique problem evidence does not match testimony
  • Common situations
  • Arson stage fire to cover
    rubbery, murder
  • Suicide/murder death may
    be alcohol or overdose
  • Burglary staged to collect

Things to consider when determining staging
  • Initially treat all death investigations as
  • Do the type(s) of wounds found on the victim
    match the weapon employed?
  • Could the wounds be easily self inflicted?
  • Establish a profile of the victim through
    interviews with friends and family
  • Evaluate the behavior ( mood and actions) of the
    victim before the event
  • Evaluate the behavior ( mood and actions) of any
    suspects before the event
  • Corroborate statements with evidential facts
  • Reconstruct the event
  • Conduct all forensic examinations to determine
    the facts of the case

  • Locards principle
  • Evidence may be direct eyewitness or
    Circumstantial does not directly prove a fact
  • Evidence can be physical or biological (trace
    can be either)
  • CSI team police officers, detectives, CSI
    investigators, medical examiners and specialists
  • CS investigation recognizing, documenting and
    collecting evidence from a scene
  • First responding officer id extent of crime
    scene (including 1 and 2), secure the scene and
    segregate witnesses
  • walk the scene, id evidence then document scene
    by photos and sketches
  • Evidence must be properly handled, collected and
    labeled to maintain Chain of Custody
  • Evidence is analyzed in a forensic lab, results
    provided to detectives who fit results into crime