Exhaustive Forensic Guide to Crime Scene Processing Evidence Handling and Scene Mapping

Initial Arrival and Evidence Identification

  • Initial Actions at Crime Scenes:

    • Upon arrival at a crime scene, an investigator must immediately scan the area, look around, and make thorough visual observations.
    • Prior to securing and collecting evidence, all distinct pieces of evidence present at the scene must be clearly identified.

  • Evidence Categories:

    • Dry evidence
    • Liquid evidence
    • Wet or moist evidence
    • Large evidence
    • Small evidence
    • Trace evidence
    • Biological evidence

Packaging and Preserving Dry Trace Evidence

  • Definition of Dry Trace Evidence:

    • Refers to minute pieces of evidence completely devoid of moisture, such as dry hairs or dry fibers.

  • Air-Drying Requirement for Moist Evidence:

    • Any evidence containing residual moisture or dampness must be fully air-dried prior to final packaging and storage.
    • Warning: Packaging wet or moist evidence directly into a sealed plastic bag creates an environment conducive to mold and fungus growth, which severely degrades and destroys the physical and biological integrity of the evidence.

  • Step-by-Step Packaging Procedure for Dry Trace Evidence:

    1. Place the dry evidence directly in the middle of a clean sheet of paper.
    2. Fold one side of the paper over the evidence along a straight fold line.
    3. Fold the opposing side of the paper over the middle.
    4. Fold the top section down and the bottom section up (continuously folding left, right, top, and bottom flaps inward).
    5. Tuck all flaps securely to form a self-contained paper square, known as a paper bindle, which fully encloses the evidence.
    6. Slide the folded paper bindle into a plastic bag.
    7. Fold the flap of the plastic bag over its opening.
    8. Apply security tape directly across the folded flap to seal the plastic bag.
    9. Sign directly over the edge of the tape and onto the plastic bag material.

  • Significance of Signing Over the Tape:

    • Establishes direct accountability by providing non-refutable, 100% confirmation of the exact individual who packaged the item.
    • Prevents evidence tampering, as removing and reapplying the tape renders it impossible to perfectly realign the broken signature lines.

Inventory Labels and Storage of Liquid and Chemical Evidence

  • Inventory Label Requirements:

    • Every packaged piece of evidence must have a completed inventory label attached to ensure efficient storage and tracking.
    • Required Fields on Inventory Label:
      • Exact physical location where the evidence was discovered
      • Specific description/type of evidence
      • Name of the suspect (if applicable)
      • Date of collection
      • Official case number

  • Packaging Liquid, Chemical, and Arson Evidence:

    • Liquid evidence, arson remains, chemical remains, and toxin remains cannot be stored in paper bindles or standard plastic/paper bags.
    • Container Specifications:
      • Must be stored in airtight, shatterproof containers.
      • Larger remains or items require larger airtight cans or specialized boxes/heavy plastic bags if excessively oversized.
      • Smaller liquid or chemical samples require smaller shatterproof containers.
    • Purpose of Airtight Sealing:
      • Prevents chemical oxidation.
      • Prevents leakage or chemical leaching into the external environment.
      • Prevents degradation of volatile compounds (such as accelerants in arson cases).

Chain of Custody Protocols

  • Definition and Importance:

    • The chain of custody is a strict, unbroken, written record documenting every individual who possesses, handles, analyzes, or interacts with a piece of evidence following its collection.
    • Because crime scene investigations lead to legal proceedings with legal consequences for perpetrators and rights for witnesses, maintaining an accurate chain of custody is essential for court admissibility.

  • Log Details on Evidence Packaging:

    • The inventory label includes a specific chain of custody section featuring sequential lines for:
      • Received from (Name/Signature of releasing party)
      • By (Name/Signature of receiving party)
      • Date
      • Time

  • Verification and Security Protocol:

    • Every handler receiving the evidence must sign across a newly placed seal over the package flap upon resealing.
    • This continuous logging and signing holds all personnel in the investigative workflow accountable and prevents loss or tampering.

Spatial Mapping and Reconstruction of Outdoor Crime Scenes

  • Establishing Scene Boundaries:

    • Outdoor crime scenes must be marked off systematically using crime scene tape, forming a defined square or rectangular perimeter (quadrant).
    • Establishing clear boundaries allows investigators to set precise reference points.

  • Datum and Sub-Datum Points:

    • A primary datum point is identified for the scene.
    • Sub-datum points are established at specific perimeter locations (e.g., designated as Corner 1).
    • Sub-datum corner points are physically marked by pounding metal rebar or wooden stakes into the ground.

  • Triangulation and Evidence Location Recording:

    • The distance of any evidence item is recorded by taking direct measurements to two fixed reference lines along the rectangular perimeter, or by measuring straight distances to two established datum/sub-datum points.
    • Because the dimensions of the perimeter square/rectangle represent known geometric values, these measurements allow exact mapping.

  • Crime Scene Reconstruction:

    • Precise spatial measurement allows investigators to reconstruct the exact physical layout of the crime scene at a later date.
    • Reconstruction is crucial if evidence is suspected to have been missed, overlooked, lost, or left behind, requiring a second analysis of the physical scene.

Forensic Laboratory Analysis and Detective Responsibilities

  • Laboratory Processing Requirements:

    • All collected evidence must be submitted to and analyzed within an accredited forensic laboratory.
    • Field testing is insufficient; complex scientific analyses—including chemical testing, toxicology screens, and microscopy—require specialized laboratory equipment.

  • Four Lead Detective Objectives for Evidence Analysis:

    1. Link Suspects to Scenes or Victims: Match physical evidence (fingerprints, blood types, DNA, hair, fibers) found at the scene to specific individuals.
    2. Identify Victims or Perpetrators: Utilize specialized tools (such as DNA profiles or dental records) to establish the identity of unknown remains or unidentified perpetrators.
    3. Corroborate or Refute Eyewitness Testimony: Compare physical evidence directly against statements given by witnesses to verify accuracy.
    4. Exonerate/Acquit Innocent Persons: Exclude individuals from suspicion when forensic analysis (DNA, fingerprints, hair analysis) fails to match them, ensuring constitutional due process.

  • Core Responsibilities of Detectives:

    • Reconstruct crime scenes in a completely objective manner driven entirely by factual evidence.
    • Share all gathered information and evidence transparently with defense attorneys representing the accused, upholding legal due process regardless of actual guilt or innocence.

Staged Crime Scenes and Investigative Procedures

  • Definition:

    • A staged crime scene occurs when a perpetrator intentionally alters or fakes evidence at a scene to mislead investigators away from the true events.
    • Analyzing staged scenes is challenging because the physical evidence was purposely placed or manipulated rather than deposited naturally during the crime.

  • Common Examples of Staged Crimes:

    • Arson: A fire intentionally set to destroy physical evidence of a primary crime, or staged to make an intentional act appear accidental.
    • Murder: A homicidal act deliberately staged to mimic a suicide.
    • Burglary: A break-in staged by a property owner to fraudulently collect insurance payouts.

  • Investigative Mindset:

    • Crime scene investigators must evaluate all physical clues objectively based on rigorous scientific facts.
    • Investigators must refrain from jumping to early conclusions or relying on subjective perceptions, which increases vulnerability to falling for the perpetrator's staged setup.