Legal Precedents, CSI Protocols, CSU Roles, and Crime Scene Processing Steps

Legal Precedents and Admissibility Standards for Forensic Evidence

  • Frye v. United States (1923)

    • Established the General Acceptance Rule for scientific evidence in court.
    • Under this standard, a scientific technique or principle must be generally accepted by the relevant scientific community to be deemed admissible.
    • In 1923, technologies like the polygraph (lie detector) were admissible under this ruling.
    • Polygraphs are no longer admissible in court today because they lack a solid scientific foundation and empirical validation, though law enforcement still uses them during investigations and interrogations.

  • Federal Rules of Evidence

    • Enacted by the federal government to create a more substantive standard than general acceptance alone.
    • Requires judges and juries to evaluate evidence based on specific scientific criteria:
      • Is there sufficient data to support the scientific field and the reached conclusion?
      • Were reliable, reproducible methods utilized?
      • Did the analysts correctly apply these methods according to standard protocol?

  • Daubert v. Merrell Dow Pharmaceuticals (1993)

    • Established the Daubert Standard, which is the governing standard for evidence admissibility in federal courts and most state courts today.
    • Superseded sole reliance on the Frye standard by establishing that general acceptance alone is insufficient.
    • Designated the judge as the explicit "gatekeeper" responsible for assessing whether forensic evidence or expert witness testimony can be admitted into court.
    • Outlined five specific criteria that evidence must satisfy for admission:
      1. Empirical Testing/Validation: The technique or theory must be tested and validated.
      2. Peer Review and Publication: The technique must be peer-reviewed and published in peer-reviewed scientific journals.
      3. Known or Potential Rate of Error: There must be an established, known error rate associated with the method.
      4. Standards and Controls: Scientific standards and protocols must exist and be actively maintained.
      5. Widespread Acceptance: The scientific technique must have gained widespread acceptance within the relevant scientific community (incorporating the core requirement of the 1923 Frye ruling).

  • Kumho Tire Co. v. Carmichael (1999)

    • Expanded the scope of the Daubert standard beyond purely scientific technique.
    • Ruled that Daubert considerations apply equally to all technical fields, non-scientific technologies, and specialized expert knowledge.

Crime Scene Contamination, Hygiene, and Media Considerations

  • Contamination Risks and CSI Misconceptions

    • Eating, drinking, or smoking at a crime scene is strictly forbidden under all circumstances, even when personnel are wearing protective gloves.
    • Risks to Investigation Integrity: Introduces foreign materials (food crumbs, discarded packaging, drink containers) that can alter the scene or be falsely documented and collected as part of the physical evidence.
    • Risks to Personnel Safety: Exposes investigators to hazardous biological contaminants (pathogens, body fluids) or toxic chemical materials present at the scene.
    • Improper Field Assessments: Non-medical personnel (investigators or detectives) must never make definitive determinations regarding cause or timing of death (e.g., assessing post-mortem animal scavenging without a certified medical examiner or deputy coroner present).
    • PPE Protocols: Individuals entering a crime scene must wear full Personal Protective Equipment (PPE). Entering a scene without gloves or shoe covers causes severe cross-contamination.

  • PPE Disposal and Personal Hygiene Procedures

    • Gloves must be put on prior to entering the crime scene perimeter.
    • Gloves must be immediately removed and properly discarded into biohazard waste containers upon exiting the crime scene.
    • Investigators must thoroughly wash their hands before consuming any food or liquids outside the scene.
    • Personnel must never lounge, rest, or sit on crime scene structures (such as dumpsters or furniture) while on duty.

  • Public Awareness and Media Exposure

    • Major crime scenes (such as homicides) regularly attract media outlets and photojournalists.
    • Crime scene investigators can be photographed or filmed unexpectedly at any time while working.
    • Real-World Example (The Oklahoman, 2007): A published news photo depicted an investigator actively picking up a purse (item of evidence) without wearing gloves while holding a coffee cup in his other hand, documenting protocol violations publicly.
    • Real-World Example (FBI Special Agent Mia): Was dispatched at 3:00 AM to process a crime scene as an AMPD investigator; media photos captured a wardrobe malfunction (unbuttoned collared shirt) during processing.
    • Strict protocol adherence is necessary both to preserve the integrity of the investigation and to prevent compromised evidence during judicial review.

Logistics and Preparation for Crime Scene Units

  • Advanced Equipment Preparation

    • Crime scene vehicles (trucks, trailers, or specialized aircraft) must remain packed and fully prepared prior to receiving a callout to facilitate rapid deployment.
    • The primary operational goal is to arrive at the crime scene as quickly as possible—typically within one hour—to prevent the loss of transient evidence.
    • Transient Evidence: Evidence that is easily lost, degraded, or destroyed by environmental elements or time (e.g., individual hairs or light fibers in windy conditions; shoe impressions in mud during heavy rain).
    • Vehicles and kits must be audited and restocked immediately following the conclusion of every crime scene processing operation.

  • Essential Gear and Supplies

    • Packaging and collection materials: Paper bags, evidence tape, permanent markers, chain of custody forms, specialized boxes.
    • Fingerprint collection: Latent fingerprint powders, fingerprint brushes, backing cards, lifting tape.
    • Measurement tools: Standard tape measures, scale rulers, survey equipment.
    • Field testing reagents: Chemical presumptive tests (e.g., Hemastix for blood detection).

  • Operational Considerations Prior to Scene Entry

    • Appropriate Attire: Standard investigator uniform includes utility/cargo pants (providing extra pockets), an agency-branded collared shirt, durable work boots, and weather-appropriate outerwear (jackets for cold conditions).
    • Lighting Assistance: Portable floodlights, spotlights, or generator systems required for nighttime scenes or indoor locations lacking electrical power.
    • Shelter Requirements: Tents, trailers, or mobile command posts to protect personnel and evidence during severe weather, extreme heat conditions (e.g., working extended hours in 105°F weather), or long-term operations (such as 36-hour rotating shifts following massive explosion scenes).
    • Hydration and Provisions: Staging area set up strictly outside the crime scene boundary stocked with water and food to prevent heat exhaustion and dehydration.
    • Scene Security: Uniformed law enforcement officers deployed to secure perimeters and prevent unauthorized access.
    • Specialist Coordination: Preemptively contacting external specialists prior to arrival (e.g., military units like Air Force specialized crime scene units; law enforcement dive teams for submerged vehicles or bodies; forensic anthropologists and medical examiners for buried skeletal remains).

The 6 Core Positions of a Crime Scene Unit

  • Staffing Distribution

    • The 6 core roles can be filled by 6 distinct individuals in large federal agencies (e.g., FBI Evidence Response Teams), split between 2 individuals in mid-sized departments (e.g., SMPD), or carried out by a single individual in smaller law enforcement agencies.

  • 1. Team Leader

    • In full operational command of the physical crime scene.
    • Operational Distinction: The Team Leader commands the scene and manages evidence collection; the Detective or Lead Investigator commands the overall criminal investigation (interviewing witnesses, interrogating suspects, determining guilt).
    • Responsibilities include:
      • Ensuring overall safety of scene personnel and verifying scene security.
      • Ensuring no active suspects or immediate hazards remain on scene.
      • Completing the Administrative Worksheet/Log (recording location, case number, personnel present, entry/exit times, initial conditions, weather, lighting, critical incidents, and final release data).
      • Drafting the comprehensive Narrative Description: A detailed written record documenting all sensory observations upon arrival (visual details, sounds, weather conditions, ambient temperature, specific smells such as fresh coffee indicating recent human presence).
      • Assigning specific roles to team members.
      • Conducting the Preliminary Survey alongside the Photographer.
      • Determining the appropriate search pattern to execute.
      • Monitoring the search and evidence collection process.
      • Performing the Final Survey (a thorough checklist audit before releasing the scene to prevent returning later to an invalidated or contaminated environment).

  • 2. Photographer

    • Visually documents the unaltered crime scene and all recovered evidence.
    • Captures specific photograph categories:
      • Entry and Exit Points: Doors, windows, gates.
      • Location Identifiers: Street name signs, house numbers, hotel signs, room numbers.
      • Overall Photographs: Standardized views of the entire scene using the Four Corners Technique (standing in each corner facing inward to capture full spatial orientation, plus central shots).
      • Mid-Range / Medium Photographs: Also termed Evidence Establishing photographs; documents the position of evidence relative to the room, the body, or other surrounding evidence items.
      • Close-Up Photographs: Fills the entire photo frame with the evidence item. Every item must be photographed twice: once without a scale and once with a scale (an L-scale ruler to document actual size without spatial distortion).
      • Specialized Photographs: Latent fingerprint impressions, footwear impressions, tire tracks.
    • Maintains a Photography Log: Records photo numbers, item descriptions, location, case numbers, and manual camera settings (aperture, shutter speed) used in complex lighting conditions. Uses photo header/identifier cards at the start of film rolls or digital sessions to separate distinct case files.

  • 3. Sketch Preparer

    • Draws physical diagrams/sketches of the crime scene (using manual measurements or computerized diagramming software).
    • Mandatory requirements for every sketch:
      • Administrative Data: Case number, date, physical location/address, investigator name, sketcher name, assistant names.
      • Orientation: A clear compass indicator showing North.
      • Scale Specification: Must state explicit scale ratios or be designated as "Not to Scale".
      • Key / Legend: Defines all symbols, numbers, or letters used (e.g., labeling a drawn rectangle as a bed or a circle as a body position).
      • Precise Measurements: Documents exact coordinate/triangulation measurements of evidence relative to fixed baseline structures (recorded on the diagram or an attached measurement table).
    • Multiple sketches must be prepared if a crime scene encompasses distinct environments (e.g., separate indoor house sketch and outdoor yard property sketch).

  • 4. Evidence Custodian

    • Stationed strictly outside the physical perimeter of the crime scene tape.
    • Maintains the master Evidence Log.
    • Receives packaged evidence directly from recovery personnel.
    • Inspects packaging seals to verify integrity and proper labeling.
    • Logs evidence details (item number matching field placards, description, precise recovery location, recovering officer name, photograph verification, packaging medium, special hazard indicators such as biohazard, firearm, or narcotics tags).
    • Secures packaged evidence in vehicles for transport to property rooms or crime laboratories.
    • Standard packaging rules: Paper bags/boxes are used for almost all evidence to prevent moisture degradation (avoiding plastic); specialized metal cans are used for arson/explosive evidence; rigid boxes are used for firearms. Indirect marking (labeling the outer packaging) is required rather than direct marking (writing directly on evidence).

  • 5. Evidence Recovery Personnel

    • Systematically search for, locate, and process evidence within the scene.
    • Place yellow numbered/lettered placards at located evidence positions.
    • Verify that photographs are taken before items are moved.
    • Package items correctly, seal containers, and apply initials and dates across package seals.
    • Hand off sealed items directly to the Evidence Custodian outside the scene perimeter.

  • 6. Specialists

    • Expert personnel requested by the Team Leader during initial planning or the preliminary survey.
    • Examples include: Underwater search/dive teams, bomb disposal technicians, forensic anthropologists, bloodstain pattern analysts, forensic entomologists.

The 12 Steps of Crime Scene Processing: Step 1 Detail

  • Overview of Processing Framework

    • Crime scene processing follows 12 structured, sequential steps to ensure thoroughness and judicial validity.

  • Step 1: Preparation

    • Executed prior to entering the actual physical scene.
    • Task Assignment: Team Leader assigns initial duties (photographer, sketch preparer, evidence recovery, custodian).
    • Legal Authorization: Securing necessary search warrants or explicit legal consent prior to entering private property.
    • Administrative Logistics: Assembling chain of custody forms, evidence log sheets, administrative worksheets.
    • Equipment Auditing: Packing packaging containers, measuring tools, camera gear, lighting equipment, and specialized field reagents.
    • Shift and Staging Planning: Establishing personnel rotations for extended processing operations and setting up off-scene support (food, water, shelter).
    • Specialist Deployment: Contacting required expert personnel to deploy to the scene.

  • Personal Protective Equipment (PPE) Guidelines in Step 1

    • Eye Protection / Goggles: Prevents eye contact with airborne particulates, biological splatters, or volatile chemicals.
    • Face Masks / Respirators: Filters airborne pathogens, chemical fumes, or dense smoke.
    • Tyvek Suits: Full-body protective suits deployed during scenes with heavy biological hazards (excessive blood/body fluids) or dangerous chemical contamination.
    • Nitrile / Rubber Gloves: Mandatory barrier protection; must be changed frequently whenever damaged or contaminated.
    • Booties (Shoe Covers): Worn over work boots to prevent leaving shoe impressions inside scenes and tracking external dirt/contaminants into the scene.
    • Dual Purpose of PPE: Acts simultaneously to protect processing personnel from dangerous environmental hazard exposure AND protect the crime scene from investigator-induced contamination (shed hair, skin cells, footwear impressions, fibers, or stray fingerprints).