Comprehensive University Study Notes on Crime Scene Investigation, Securing, Documentation, Search Techniques, Evidence Collection, and Chain of Custody

Four Primary Steps of Crime Scene Investigation

Crime scene investigation follows a structured sequence designed to preserve evidence integrity, document spatial relationships, and maintain legal defensibility:

• Step 1: First Response – Initial response, scene securing, and threat mitigation.
• Step 2: Initial Assessment & Searching – Preliminary scene evaluation, formal walkthrough, strategy formulation, and systematic searching.
• Step 3: Collection & Processing – Presumptive testing, documentation, evidence packaging, and preservation.
• Step 4: Final Assessment – Scene audit, final tasks, hazard reporting, and official scene release.

National standards and operational recommendations are established by bodies such as the National Institute of Standards and Technology (NIST).

First Response and Initial Scene Management

Dispatch and Arrival Triggers

Investigators and response personnel are dispatched to a crime scene through three main scenarios:

• Emergency Call Dispatch: A citizen or witness calls emergency services, prompting the dispatch of a police patrol unit. EMS and Fire services are dispatched simultaneously as needed.
• Patrol Encounter: Patrol officers encounter a crime or suspicious scene during routine duty, investigating independently until additional specialized assistance is required.
• Search Warrant Execution: A search warrant is issued by a judicial authority, resulting in the simultaneous dispatch of police officers, detectives, and Crime Scene Investigators (CSIs).

Primary Duties of the First Responder

The first officer on scene must execute critical tasks without introducing contamination:

• Approach and Enter Scene: Access the location safely while noting initial environmental conditions.
• Check for Immediate Threats: Identify and neutralize hazards to life and scene integrity.
• Provide Emergency Care: Administer immediate medical assistance to injured individuals.
• Control People at the Scene: Manage bystanders, witnesses, and potential suspects.
• Establish Preliminary Boundaries: Define physical boundaries to secure the core location.
• Document Actions: Maintain precise records of all personal actions and observations taken upon arrival.
• Turn Over Control: Hand operational command over to the lead investigator upon their arrival.

Categorization of Immediate Threats

First responders must prioritize threat mitigation in the following order:

• Threats to Victims: Active, ongoing criminal activity or acute physical trauma requiring immediate medical intervention.
• Threats to Personnel: Armed or dangerous culprits (in active shooter incidents, containing the threat is the absolute first priority), biohazards, chemical hazards, and physical hazards.
• Threats to Case Integrity: Escape of the culprit, destruction or physical degradation of evidence, loss or dispersion of eyewitnesses.

Crowd Control Protocols

Proper crowd control isolates the scene from external interference:

• Identification of Scene Individuals: Categorize everyone present into distinct groups: Suspects, Witnesses, Victims/Family/Friends, Bystanders, and Medical personnel.
• Exclusion: Bar all unauthorized individuals from entry.
• Eyewitness Isolation: Immediately separate eyewitnesses from one another to prevent memory contamination, collaborative story formulation, or bias.

Scene Securing, Boundary Establishment, and Command Post

Physical Securing Methods

To prevent contamination, physical access control tools direct human movement:

• Crime scene tape.
• Ropes or traffic cones.
• Floor tape walkways (used indoors to designate precise footpaths).

Boundary Establishment Criteria

Boundaries must be established based on spatial relevance:

• Locations to Include:
  • The primary scene where the central criminal event occurred.
  • All secondary scenes connected to the event.
  • Points and paths of entry and exit used by perpetrators or victims.
  • Locations where the victim or physical evidence may have been moved.
  • Any location where it is reasonably likely that the culprit walked, drove, or touched surfaces.
• Locations to Exclude: High-traffic public areas unnecessary to the investigation and physical locations that are completely inaccessible.

Command Post Establishment

A Command Post is established outside the secure crime scene zone (often utilizing specialized mobile command post units) to function as:

• Communication Nexus: A centralized hub to share information, assign duties, and dispatch specialized units.
• Equipment Holding Area: Staging site for tools, processing kits, and scientific equipment kept outside the secure perimeter until needed.
• Rest Area: Designated operational break zone for investigative personnel.

Roles and Qualifications of Crime Scene Investigators

Crime Scene Investigators (CSIs) operate as either sworn police officers or educated civilian professionals:

• Educational Requirements: High School Diploma/GED or a Bachelor of Science ($BS$) degree.
• Salary Range: Approximately \\text{\30,000} - \\text{\60,000}\,\text{per year}.
• Background Requirement: Must maintain a clean background check record.

Preliminary Assessment and Formal Walkthrough (Initial Reconstruction)

Preliminary Assessment

The preliminary assessment addresses the fundamental operational question: "What do I need to do?"

• Debrief initial first responders.
• Evaluate scene safety needs.
• Review and adjust initial physical boundaries.
• Designate explicit walkways and entry paths through the scene.

Formal Walkthrough (Initial Reconstruction)

The formal walkthrough addresses the core investigative question: "What happened here?" Specific factors evaluated include:

• Crime Identification: Determination of what specific crime, if any, occurred.
• Entry and Exit Points: Assessment of entry points and whether doors or windows are open, locked, or unlocked.
• Disturbance and Damage: Assessment of physical damage, displaced furniture, or indicators of a physical struggle.
• Activity Indicators: Evidence of daily living activities (e.g., prepared meals, ongoing cleaning, active television sets, illuminated lights).
• Temporal Indicators: Time and date indicators such as uncollected mail, product expiration dates, or rotten food.

Walkthrough Outcomes

The walkthrough establishes strategy, answering: "What is the most effective way to process the scene?"

• Prioritize areas for immediate evidence processing.
• Divide tasks among available investigators.
• Select specific diagnostic tools, chemical tests, and processing equipment.
• Select the optimal systematic search pattern.
• Identify the need for specialized personnel (e.g., bloodstain pattern analysts, forensic entomologists).
• Refine or adjust physical scene boundaries as necessary.

Comprehensive Crime Scene Documentation

Administrative Logs

• Crime Scene Entry/Exit Log Form: Required record of all individuals entering the scene. Must document name, title, agency, location, initials, date and time in, date and time out, and reason for entry. Security personnel assigned to scene security must log in and out, listing their reason as "Log Officer".
• Evidence Recovery Log Form: Required record of all physical items recovered. Captures item number, recovered by (name), detailed description, initials, date, and time. The evidence log officer must sign and date the log directly below the final item entered.

Crime Scene Field Notes

Field notes must be written concurrently at the scene and capture:

• WHEN: Precise dates and times of arrival, actions, and departures.
• What you DID: Complete procedural actions taken.
• What you OBSERVED: Detailed physical descriptions of the scene and evidence.
• WHO: Names and roles of all individuals worked with.

Crime Scene Photography Standards

Photography is the single most important documentation tool. It requires adequate size/resolution, appropriate focus, and adequate illumination. Photographs fall into four distinct categories:

• Long-Range Photographs: Taken from distances greater than $3\,m - 5\,m$ ($> 3\,m - 5\,m$). Displays overall scene context and spatial orientation.
• Mid-Range Photographs: Taken from distances between $1\,m - 3\,m$ ($1\,m - 3\,m$). Groups multiple pieces of evidence or highlights a specific section of the scene.
• Close-Up Photographs: Taken at distances less than $1\,m$ ($< 1\,m$). Focuses exclusively on details of a single item of evidence.
• Examination Quality Photographs: Macro or extreme close-up photography containing scale markers, providing sufficient detail for individualization analysis (e.g., fingerprint or footwear impression comparison).

Crime Scene Sketches and CAD

Sketches document spatial relationships between pieces of evidence without visual clutter:

• Advantages: Eliminates graphic gore, is not restricted by visual line-of-sight obstacles, and simplifies complex physical spaces into a single coherent image.
• Formats: Hand-drawn floor plans, elevation views, perspective views, and Computer-Aided Drawing (CAD) models.
• Required Header and Legend Information: Case number, artist name, physical address/location, date, time, orientation (North arrow), and numbered evidence key.

Crime Scene Videography

• Provides the clearest visual demonstration of continuous physical paths through a scene.
• Resolution is generally lower than professional still photography.
• Must include an introductory segment stating basic case details.
• Must be recorded with no narration and no microphone audio to prevent recording off-topic or improper comments.

Crime Scene Search Techniques and Detection Tools

Systematic Search Patterns

• Zone Search:
  • Description: Scene is divided into distinct quadrants or zones.
  • Pros: Functions exceptionally well for solo investigators; easily adapts to small or irregular indoor spaces.
  • Cons: Can be difficult to establish clear zones in featureless environments; can be inefficient.
• Line / Strip Search:
  • Description: Searchers walk parallel paths along defined strips in one direction.
  • Pros: Highly effective for large outdoor areas and irregular terrain.
  • Cons: Requires multiple searchers to execute effectively; requires at least one defined straight boundary.
• Grid Search:
  • Description: Two sequential line searches executed at right angles ($90^\circ$) to one another.
  • Pros: Extremely thorough search method.
  • Cons: Requires multiple people; highly time-consuming; requires distinct boundaries; awkward in small enclosed spaces.
• Spiral Search:
  • Description: Searcher moves in a continuous circular path, spiraling either inward from boundary to center or outward from center to boundary.
  • Pros: Easy to execute by a single investigator; highly effective at detecting physical entry and exit paths.
  • Cons: Awkward to execute indoors; mathematically difficult to maintain a perfect spiral.
• Wheel / Ray Search:
  • Description: Searchers move outward or inward along straight linear rays originating from a central focal point.
• Link Method:
  • Description: Follows logical connections between individual items of physical evidence, moving dynamically from one item to the next based on spatial and contextual relevance.

Physical Evidence Detection Tools

• Alternative Light Source (ALS): Emits high-energy light causing specific materials to fluoresce. Filters out background light to reveal biological stains, broken glass fragments, hair, and fibers.
• Field Color Testing (Presumptive Chemical Testing): Field chemical tests (such as the phenolphthalein test for blood) provide rapid identification of unknown substances. These tests carry higher error rates than formal laboratory assays and must be performed on both the suspected stain and an adjacent unstained control area.
• Fingerprint Dusting: Powder application that binds to skin oils to reveal latent (invisible) friction ridge impressions.

Evidence Marking Protocol

Every item that might reasonably constitute evidence must be marked with a numbered physical marker and photographed in place to demonstrate context within the overall scene.

Evidence Collection, Packaging, and Preservation Guidelines

General Collection Protocols

• Goal: Preserve physical evidence intact without introducing contamination.
• Precautions: Investigators must wear clean gloves, use forceps, or wear protective masks when handling items.
• Documentation: Conduct field tests, record results in notes, and photograph presumptive test results and areas yielding negative fingerprint dusting results.
• Isolation: Package all evidence items individually in appropriate containers.

Criteria for Appropriate Containers

Packaging choices must meet five standard criteria:

• Protects operational personnel from harm (e.g., puncture hazards).
• Protects evidence against physical damage.
• Protects against leakage of liquids or trace material.
• Fits the physical dimensions of the item comfortably.
• Represents the lowest possible cost for the required preservation task.

Handling Biological Evidence

Biological fluids include saliva, semen, blood, urine, feces, and vomitus.

• Environmental Hazards: Biological materials degrade rapidly when exposed to bacteria, fungus, and ultraviolet (UV) light.
• Core Storage Rules: Keep dry, keep dark, and keep cold.
• Packaging Procedures by State:
  • Individual Liquid Stains: Swab using a clean swab, allow to air dry completely, and package inside a cardboard swab box.
  • Wet Stains on Fabric: Wrap the item in plain paper, package it inside a outer paper container, and allow it to air dry flat.
  • Dry Stains on Fabric: Package directly inside breathable paper packaging.

Specialized Packaging Guidelines by Evidence Type

Final Assessment and Scene Release Procedures

Prior to releasing command of a crime scene, the lead investigator must complete a final assessment:

• Verify that all targeted physical areas have been thoroughly searched.
• Cross-check physical evidence packages directly against evidence logs.
• Determine final counts and types of evidence collected.
• Assign remaining final processing tasks to team members.
• Clean up operational refuse and trash generated during processing.
• Report any persistent physical, chemical, or biological hazards.
• Formally release the crime scene.

Chain of Custody Protocol and Implementation

Definition and Principles

The chain of custody is the continuous, unbroken, chronological documentation showing the seizure, physical control, transfer, analysis, and disposition of evidence. An identifiable individual must maintain secure physical custody of every piece of evidence at all times.

Exemplary Chain Transfer Progression

$\text{Suspect} \rightarrow \text{CSI Leela} \rightarrow \text{Evidence Clerk Zoidberg} \rightarrow \text{Technician Fry} \rightarrow \text{Analyst Farnsworth} \rightarrow \text{Attorney Rodriguez} \rightarrow \text{Court} \rightarrow \text{Evidence Clerk Zoidberg} \rightarrow \text{Evidence Clerk Zoidberg}$

Foundation Information on Packaging

Every evidence package must feature an intact chain-of-custody tracking block containing:

• Case Number.
• Item Number.
• Detailed Item Description.
• Date and Time of Collection.
• Name and Badge/ID Number of the Collector.
• Tamper-proof Seal (signed across the edge of the tape seal).

Implementation Methods

Chain of custody documentation is maintained via:

• Direct printing on the exterior of paper packaging.
• Adhesive chain-of-custody labels affixed to containers.
• Standalone physical paperwork forms.
• Laboratory Information Management System (LIMS) barcode tracking.

Secure Physical Storage Facilities

During retention, physical evidence must be secured inside:

• Locked cabinets or drawers.
• Individual secure storage lockers.
• Locked evidence rooms restricted to designated evidence control officers.

Consequences of Chain Maintenance Failure

If the chain of custody is compromised:

• The evidence becomes legally inadmissible in court proceedings.
• The responsible officer or analyst may be terminated.
• The crime laboratory may face formal accreditation sanctions.
• The professional reputations of all involved personnel are severely damaged.

Final Evidence Disposition

Once legal proceedings conclude, evidence undergoes one of four final outcomes:

• Permanent retention by the police agency.
• Return to its lawful owner.
• Legal forfeiture.
• Complete destruction.

Evaluative Summary of Crime Scene Investigation Operations

Operational Strengths

• Standardized protocols ensure uniform preservation and location of physical evidence.
• Safety protocols protect investigators from biohazards and physical scene dangers.
• Heightened awareness minimizes cross-contamination risk.
• Rigorous documentation and unbroken chain-of-custody requirements ensure constitutional fairness during judicial trials.

Operational Limitations and Pitfalls

• Errors made at the crime scene caused by ambient background noise, distraction, or initial mis-identification are typically irreversible.
• Complex or extensive scenes introduce overlapping, confusing operational tasks.
• Not all forensic evidence present at a scene will successfully be discovered or recovered.
• Investigators do not always adhere strictly to required standards of evidence collection and chain of custody maintenance.