You Can't Touch This - Documents and Trace Evidence

Chain of Custody

• Definition: Chronological documentation or paper trail showing the seizure, custody, control, transfer, analysis, and disposition of physical or electronic evidence.
• Importance: An unbroken chain of custody is crucial. If broken, the defendant can request that the evidence be declared inadmissible.
• Packaging of evidence: Different evidence types have different packaging requirements. For instance:
  • Ignitable liquid residues: Must be kept airtight to contain volatiles.
  • Clothing: Should be collected in brown paper bags to allow breathability and prevent mold.
  • Dangerous items (e.g., glass controls): Should be in plastic pots.
  • Fragile items (e.g., light globes): Packaged to prevent further damage during transfer.

Trace Evidence

• Definition: Evidence resulting from contact between different objects.
• Characteristics:
  • Often not visible to the naked eye.
  • Examples: Fingerprints, hairs, cosmetics, synthetic fibers, glass, paint chips, etc.
• Purpose:
  • Fingerprints and DNA: Identify individuals present at a scene (who).
  • Trace evidence (paint, fibers, glass): Provide activity context (how/why).
• Locard's Exchange Principle: "Every contact leaves a trace." There will always be some transfer between two items in contact.
• Collection Methods: Vary based on evidence type.
  • Hand picking
  • Tape lifting
  • Shaking
  • Other methods

Forensic Paint Examination

• Definition: Examination of paint evidence from forensic cases.
• What is paint?: Coating used to decorate, protect, add color, luster, or smooth an item.
• Types: Architectural, vehicle, etc.
• Cases: Vehicle collisions, break-ins, graffiti, etc.
• Transfers: Usually occur due to heat or friction, leaving smears or chips.
• Directionality: One-way or two-way transfers are possible (e.g., in vehicle collisions).
• Steps in Comparison:
  • Optical microscopy: Most revealing, examines paint layers.
  • Infrared microscopy: Identifies binder types, fillers, and pigments, requires understanding of paint technology and polymers used.
  • UV Vis: Objective color comparison, measures wavelength of light reflected.
    • Cannot analyze black, white, and gray.
    • Can identify UV absorbers in clear coats.
    • $UV \ visible \ spectrum$
  • Scanning Electron Microscope (SEM) with Energy Dispersive X-ray Analysis (EDX):
    • Determines elemental composition.
    • Nondestructive.
    • Identifies extenders/pigments (e.g., titanium dioxide, talc).
• Practical Forensics:
  • Controls: Adequate and representative samples are critical.
    • Collect from areas close to damage.
    • Compare like with like.
  • Significance: Depends on color, composition, and number of layers.
    • Original Equipment Manufactured (OEM) will have about four layers.
    • Older vehicles may have more layers, higher evidential value, given multiple repaints.
    • Common white paint may be of limited evidential purposes.
  • PDQ Database: International database (Mounted Police in Canada) to identify vehicle make/model from paint samples.

Glass Examination

• Backscatter Fragmentation: When glass breaks, fragments are scattered back towards the breaker.
• Aim: Compare glass from a broken window or container to recovered glass from a suspect's clothing or tools.
• Cases: Break-ins, assaults, homicides, motor vehicle collisions.
• Analytical Techniques:
  • Refractive Index: Bending and slowing of light as it passes through a transparent object.
    • Measured using GRIM (Glass Refractive Index Measurement).
    • Oil immersion variable temperature method for tiny fragments.
    • Measures to five decimal places.
  • Elemental/Chemical Characteristics: Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS).
    • Destructive.
    • Provides higher discrimination than refractive index.
    • Measures percentages of elements (silicon, iron, etc.).
• Significance:
  • Glass is not generally found on random individuals.
  • Persistence is important (glass is lost readily).
  • Smartphone glass is a different type.
  • Databases for elemental composition and refractive index.
  • Refractive index most common if 1.519.
• Statistics:
  • Bayesian statistics.
  • Likelihood ratio to convey probability of evidence given competing hypotheses.

Fiber Examination

• Cases: Homicides, sexual assaults, assaults, break-ins.
• Evidential Value: White cotton and blue denim fibers have lower value.
• Transfer: Fibers transfer readily, but if there's legitimate contact, there’s no evidential value.
• Infamous Cases:
  • Louise Bell disappearance.
  • Wanaka homicide.
  • Daniel Hind homicide: Fibers from victim’s shoes matched carpet in residence.
  • Richard Kelvin homicide:
    • Nine distinct groups of fibers found on victim’s clothing.
    • Fibers matched sources in suspect's environment (carpet, cardigan, bedspread).

Document Examination

• Definition: Comparison of unknown documents with known documents.
• Purpose: Connect or exclude an individual from a crime.
• Types of Examinations:
  • Handwriting and signatures.
  • Paper analysis.
  • Ink analysis.
  • Detection of erasures or alterations.
• Cases: Homicides, drug trafficking notebooks, etc.
• Handling: Protect documents in plastic bags or envelopes and prevent folding.
• Fingerprinting: Can damage documents; coordinate with fingerprint examiners.
• Techniques:
  • Electrostatic Detection Apparatus (ESDA): Reveals indented impressions.
  • Microscopy and different lighting techniques.
• Signature Comparison:
  • Request specimen signatures from individuals.
  • Collect specimens from daily activities (banking forms, etc.).
• Case Examples:
  • Snowtown case: Forged signatures on Centrelink documents provided a timeline for when people went missing.
  • Mark Rust case: Letter directing police to the body was compared to suspect’s writing.
• Printing Processes: Counterfeit checks or currency.
  • Compare features (opaque window, background print, microprinting).
• Alterations: Addition of text, like on checks.
  • Use infrared fluorescence to discriminate between inks.
• Obliterations: Use infrared or fluorescent lighting to uncover scratched out writing.
• Chemical Erasure: Chemicals (e.g., brake fluid) used to remove ink from documents.
  • Leaves the check blank once the ink is removed.
• Document Restoration: Reassembling shredded or torn documents.