#6 - crime scene

Crime Scene Basics

  • Physical Evidence

    • Indicates a crime was committed

    • Supports or rejects witness testimony

    • Links suspect with victim or crime scene

    • Assists in determining identity of individuals involved

    • Allows for re-creation of the crime

  • Finding the Modus Operandi

    • Examination and search techniques in major cases

    • Reference: Safferstein-Criminalistics

Definition of a Crime Scene

  • Classification by Location:

    • Primary: Initial site where the crime occurred.

    • Secondary: Where the body is disposed after the crime (e.g., woods).

    • Tertiary: Any subsequent crime scene following a secondary scene.

Dynamic Nature of Crime Scenes

  • Crime scenes begin to change immediately after the crime occurs.

  • Delay in investigation results in less resemblance to the original scene.

Interaction of Investigator and Crime Scene

  • Investigator's presence can alter the crime scene.

  • Alterations can be minimal or major.

  • Changes may be deliberate or unconscious.

Indicators of a Crime

  • Normal observations may show no unusual features.

  • Use of luminol for presumptive blood testing can reveal hidden blood traces.

Crime Scene Investigation Principles

  • Based on the scientific method and Locard's Exchange Principle (LEP).

    • LEP: Contact between items results in evidence exchange.

    • Foundation for trace evidence collection.

Types of Evidence

  • Testimonial Evidence:

    • Includes oral and written statements from witnesses.

  • Physical Evidence:

    • Material items present at the crime scene or on individuals.

  • Trace Evidence:

    • Found in small, measurable amounts (e.g., hair, fibers).

  • Transient or Conditional Evidence:

    • Changeable evidence (e.g., temperature, smells).

    • Might be compromised or lost over time.

Types of Physical Evidence

  • Questioned Evidence: Arises from the crime scene.

  • Control Evidence: Comes from known sources (victims, suspects).

Examples of Crime Object and Suspect Object

  • Examples of Crime Objects:

    • Fibers on a victim's body

    • Fingerprints found at the scene

    • Bullets recovered from a body

  • Examples of Suspect Objects:

    • Known blood samples from suspects

    • Carpet fibers from a suspect's home

Role of Forensic Chemist in Investigations

  • Collaborate with detectives to understand investigative needs.

  • Help formulate questions surrounding the crime.

  • Gather information and evidence relevant to the case.

Investigation Planning

  • Determine what to search for and how to preserve evidence.

  • Assess needs for specialists or equipment.

  • Keep an open mind regarding evidence.

Crime Scene Procedures

  • Prioritize evidence collection while doing no harm.

  • Prevent changes to the scene that could compromise evidence.

The Seven S’s of Crime Scene Investigation

  1. Secure the Scene

  2. Separate the Witnesses

  3. Scan the Scene

  4. See the Scene

  5. Sketch the Scene

  6. Search for Evidence

  7. Secure and Collect Evidence

Securing the Crime Scene

  • Initial officer's responsibilities:

    1. Provide medical assistance to victims.

    2. Detain potential suspects.

    3. Secure the crime scene area.

    4. Call for additional personnel as needed.

  • Must establish boundaries using tape, ropes, cones; keep logs of personnel movements.

Preliminary Examination Steps

  • Conduct a “walk-through” for initial documentation.

  • Use videotaping, photography, sketches, and notes conducted effectively to capture the scene.

    • All objects should remain unaltered during this process.

Photography Best Practices

  • Overview photographs:

    • Objects should not be moved prior to photography.

  • Various angles captured including midrange and close-ups.

  • Measuring tools should be incorporated for reference.

Sketching the Scene

  • Accurate measurements of all elements including doors, windows, and evidence.

  • Triangulation and rectangular coordinate methods for accuracy in placement.

Importance of Recording & Maintaining Evidence

  • Must document all findings meticulously for use in investigations and trials.

  • Limited time exists to note conditions prior to disturbance.

  • Importance stemming from accurate scene representation for proceedings.

Methods of Searching for Evidence

  • Search Strategies:

    • Line or Strip Method: Ideal for large, open areas.

    • Grid Method: Double-line search; thorough but time-consuming.

    • Zone Method: Effective in smaller areas; teams assigned specific zones.

    • Spiral Method: Suitable for circular settings; moves inward or outward.

Evidence Collection Protocol

  • Use separate containers for different items to avoid contamination.

    • Correct packaging crucial for maintaining the integrity of evidence (e.g., use of airtight for biological items).

  • Follow strict chain of custody protocols to ensure evidence is admissible in court.

Chain of Custody Requirements

  • Maintain detailed records of possession and transfer of evidence.

  • Important factors:

    • Date and time of transfer

    • Location

    • Names involved

    • Purpose of transfer