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Forensic Science. Criminalistics Chapter 2 The Crime Scene. Physical Evidence. 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. The Value of Physical Evidence.

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Forensic Science

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forensic science

Forensic Science


Chapter 2

The Crime Scene

physical evidence
Physical Evidence

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

the value of physical evidence
The Value of Physical Evidence

Physical Evidence is only valuable when collection is performed with selectivity that is determined by the collector’s knowledge of the capabilities of the crime lab

forensic science begins at the crime scene
Forensic Science begins at the Crime Scene

Physical evidence must be recognized and properly preserved for lab examination or it is useless to investigators and/or prosecutors in a court of law

securing and isolating a crime scene
Securing and Isolating a Crime Scene

Duties of the Arriving Officer:

  • Get medical attention for suspect or victim
  • Arrest perpetrator if remaining on premises
  • Secure the Crime Scene
securing and isolating a crime scene1
Securing and Isolating a Crime Scene
  • The Arriving Officer must prevent unauthorized or unneeded access:
    • Unnecessary police officers
    • Neighbors/Onlookers
    • Members of the Media

Every individual entering a crime scene can potentially destroy important evidence

Once the crime scene has been secured, a Lead Investigator begins the process of evaluating the immediate area as well as adjacent areas to the crime scene.
evaluate the crime scene
Evaluate the Crime Scene
  • The Lead Investigator will:
    • Determine the boundaries of the scene
    • Document and photograph obvious evidence
    • Develop a strategy for a systematic examination and documentation of entire scene
record the crime scene
Record the Crime Scene
  • Accurate records are important for investigators and prosecutors
    • Useful in subsequent investigations
    • Document the exact condition of crime scene
    • Mark exact location of physical evidence
methods of crime scene recording
Methods of Crime Scene Recording
  • Photography & Videography
    • May be limited by budget/personnel
  • Detailed Sketches with accurate measurements
  • Detailed Notetaking with descriptions of evidence collected
crime scene photography
Crime Scene Photography
  • The crime scene must be unaltered and in the original state found by investigators
  • Must be photographed from all necessary angles
  • Evidence must not be moved prior to photography: if it has been moved, it cannot be reintroduced into the scene for photo purposes
crime scene photography1
Crime Scene Photography
  • Photos must be taken of the entire room and all rooms adjacent to initial crime scene
  • Close-up photos and panoramic photos are taken and sometimes include a ruler for scale
  • All pieces of physical evidence are photographed prior to removal
crime scene videography
Crime Scene Videography
  • Increasingly popular due to cost
  • Long-shots and close-ups are taken of scene
  • Narrations are often included as a method of note-taking
crime scene sketching
Crime Scene Sketching
  • Rough Sketch:
    • An accurate depiction of dimensions of the scene, showing the location of all objects that may have implications to the crime
rough sketches
Rough Sketches
  • Objects are depicted from two fixed locations at the scene
  • Accurate measurements must be taken with a tape measure
  • Sketch evidence by using letters or numbers and a legend at the bottom
  • Sketch should always depict the NORTH direction
finished sketch
Finished Sketch
  • A precise depiction of the crime scene, drawn to scale
  • Sometimes drawn with the aid of a computer
    • CAD: Computer-aided drafting
notetaking at a crime scene
Notetaking at a Crime Scene
  • Constant activity at a crime scene that includes the following:
    • A written description of the scene in a narrative format
    • Location of physical evidence items recovered
      • Time evidence discovered and by whom
      • The condition of the evidence recovered
notetaking at a crime scene1
Notetaking at a Crime Scene
  • Tape Recording may also be used to record a crime scene
  • Videotaping a scene with narration may also be used
  • All tape/video recordings must be transcribed onto paper for recordkeeping
search for evidence
Search for Evidence
  • Must be thorough and systematic
  • How the search is carried out depends on the location and size of the area and the actions of the suspect(s) and victim(s)
typical types of crime scene searches
Typical types of Crime-Scene Searches

Spiral Search Method: Begins from one point of the crime scene and continues in a spiral fashion to another point

typical types of crime scene searches1
Typical types of Crime-Scene Searches
  • Strip or Line Search: Several investigators begin side-by-side and search in a straight line and turn around and continue back on an adjacent part of the area
typical types of crime scene searches2
Typical types of Crime-Scene Searches
  • Grid Search: Investigators begin a search in an S-pattern from the a border of a crime scene and overlap the S-pattern on return
typical types of crime scene searches3
Typical types of Crime-Scene Searches
  • Quadrant or Zone Search: Investigators divide crime scene into four sections then search one section at a time until the entire area has been searched
typical types of crime scene searches4
Typical types of Crime-Scene Searches

What type of search conducted depends on:

  • Size of the crime scene
  • Complexity of the crime scene
  • Manpower available to conduct the search
physical evidence at a crime scene
Physical Evidence at a Crime Scene
  • Can be macroscopic to microscopic
  • Trace evidence may be found on clothing, in automobiles, etc.
  • All items must be handled and packaged with care to preserve the evidence
physical evidence at autopsy
Physical Evidence at Autopsy
  • Items routinely sent to the crime lab:
    • Victim’s clothing
    • Fingernail scrapings
    • Head and pubic hairs
    • Blood (for DNA typing)
    • Vaginal, anal, and oral swabs for sex crimes
    • Recovered bullets from body
    • Hand swabs from shooting victims for gunshot residue
collecting and packaging evidence
Collecting and Packaging Evidence

Physical evidence must be collected and packaged carefully to prevent contamination, breakage, evaporation, and accidental scratching and/or bending.

integrity of evidence
Integrity of Evidence
  • Blood, hairs/fibers, soil and dust should be submitted intact and should not be removed from garments or surfaces
    • When these items are found on large objects that cannot be removed easily, evidence can be removed carefully using forceps or swabs
integrity of evidence1
Integrity of Evidence
  • Each different item or similar items collected at different locations must be placed in separate containers
    • Prevents damage
    • Prevents cross-contamination of specimens
packaging evidence
Packaging Evidence
  • Use forceps for picking up small items
  • Use unbreakable plastic bottles with pressure lids for hair, glass, fibers, and other small trace evidence
    • Manila envelopes and screw-cap glass containers may also be used for trace evidence
    • “Druggist-fold” Envelopes may also be used
packaging evidence1
Packaging Evidence
  • Use wrapping paper, manila envelopes, paper bags are used for blood stained material
    • Airtight containers are never used because they can readily grow molds and destroy evidence
    • Airdry wet/bloody clothing and place in paper bags
packaging evidence2
Packaging Evidence
  • Use airtight containers for charred evidence from fires
    • Prevents evaporation of accelerant
    • Common packaging:
      • Empty, unused paint cans
      • Tightly sealed jars
chain of custody
Chain of Custody
  • A list of all persons who came into possession of an item of evidence
  • May include: collector, carrier, lab tech, evidence storage officer, investigator, medical examiner, etc
  • Unnecessary personnel should not handle evidence without justification prevents contamination
standard reference samples
Standard/Reference Samples
  • Physical evidence whose origin is known, such as blood or hair from a suspect, that can be compared with crime scene evidence
  • Used as a comparison method to incriminate or exonerate a suspect or to identify a victim
submitting evidence to a lab
Submitting Evidence to a Lab
  • May be completed by delivery or by mail
  • Should be done by someone familiar with the case
  • Includes an “Evidence Submission Form” stating the case history and type of exam requested
  • Must maintain Chain of Custody in all cases
crime scene safety
Crime Scene Safety
  • Increased risk of AIDS and Hepatitis B infection to responding officers at a crime scene
  • Precautions must be taken for officers to protect themselves from all types of hazards
crime scene safety ways to reduce risks
Crime Scene Safety: Ways to Reduce Risks
  • Wear double gloves, protective footwear and clothing
  • Use masks/respirators, goggles or face shields
  • Be alert to sharp objects such as knives, needles, razor blades, etc.
  • Dispose of contaminated objects such as soiled gloves and clothing items that were worn by personnel
crime scene safety ways to reduce risks1
Crime Scene Safety: Ways to Reduce Risks
  • Complete notetaking with uncontaminated gloves to prevent contamination of pens and notebooks
  • Remove torn or contaminated material and discard immediately
  • No eating, drinking or smoking at the scene
  • All nondisposable linens or clothing should be labeled and laundered properly
legal considerations at the crime scene
Legal Considerations at the Crime Scene
  • All removal of evidence from a person or from the scene must conform to the Fourth Amendment:

The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, 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.

warrantless searches
Warrantless Searches
  • Existence of emergency situations
  • Prevent the immediate loss or destruction of evidence
  • Search of a person or property following a lawful arrest
  • Search by consent
mincey v arizona
Mincey v. Arizona
  • After a homicide, police searched a scene for four days. Evidence collected was found to be inadmissible in court because the court did not feel that evidence would have been lost or destroyed in the time needed to obtain a legal search warrant.
michigan v tyler
Michigan v. Tyler
  • Fire destroyed a building and evidence was collected the first day at the scene. After the initial entry, later entries into the building produced evidence. All evidence from later entries to the property were deemed inadmissible in court.