Unit 1: Understanding crime scene

A crime scene is any physical location where a suspected offence has occurred or where evidence of that offence may be found. It is the primary source of physical evidence linking a suspect, a victim and an act, and its value depends entirely on how it is recognised, protected and recorded. Modern crime scene work rests on Locard's Exchange Principle (Edmond Locard, c. 1910), which holds that every contact leaves a trace.

Defining properties that later sections rely on:

• Transfer: every contact between two surfaces exchanges material (fibres, hair, prints, biological fluids); the scene is a record of these transfers.
• Fragility: physical evidence is perishable and easily lost, altered or contaminated; time works against the investigator.
• Chain of custody: an unbroken, documented record of who handled each item, when and where, must exist from collection to court.
• Reconstruction goal: the scene is processed to answer what happened, how, when, in what sequence, and who was involved.
• Legal admissibility: evidence is useful only if collection, documentation and handling withstand judicial scrutiny.

II. Introduction to Crime Scene

What a scene is and the principles that govern work at it.

A. Definition and scope

The scene is the focal point of an investigation and the source of corroborative physical proof.

• Locus: the place of occurrence — indoor, outdoor, a vehicle, or a body itself; boundaries extend to entry and exit paths.
• Evidence types: transient (odour, temperature), conditional (lighting, door position), pattern (bloodstains, tyre marks), and transfer (trace material moved between surfaces).
• Purpose: to establish the corpus delicti, connect or exclude suspects, and support witness accounts with objective data.

B. Guiding principles

• Locard's principle: trace transfer means absence of evidence is not evidence of absence — search thoroughly.
• Minimal disturbance: move through the scene along a single path; touch nothing until documented.
• Contamination control: use gloves, masks and single-use tools to prevent adding or removing material.

III. Types of Crime Scene

Classification determines the search strategy and resources required.

A. Classification by boundary and access

• Primary scene: where the offence actually occurred and evidence is densest — e.g. the room where a body is found.
• Secondary scene: a linked location holding related evidence — e.g. the vehicle used to move the body, or a disposal site.

B. Classification by environment and nature

• Indoor vs outdoor: indoor scenes are more controllable; outdoor scenes are exposed to weather, animals and public access, so require urgent protection.
• By offence: homicide, burglary, arson, sexual assault, hit-and-run — each dictates specific evidence expectations (e.g. accelerant residue in arson).
• Macroscopic vs microscopic: the visible layout (bodies, weapons, furniture) versus trace-level material (hairs, fibres, gunshot residue).

IV. Evaluating the Crime Scene

The assessment made before any evidence is touched.

A. Preliminary survey

• Walk-through: the investigator makes an initial cautious tour to grasp scale, note transient evidence and plan the search.
• Focal points: identify the point of entry, point of exit, the centre of activity and likely evidence-bearing surfaces.
• Theory formation: develop a tentative, revisable hypothesis of events to guide search without biasing it.

B. Determining boundaries and hazards

• Boundary setting: define an area generous enough to include approach paths; boundaries can be shrunk later but not reliably expanded.
• Safety: assess biohazards, firearms, fire, structural danger and electrical risk before entry.

V. Processing the Crime Scene

The systematic sequence that turns a location into recorded, collected evidence.

A. Sequence of operations

Processing follows a fixed order so that recording precedes disturbance.

• Secure → evaluate → document → search → collect → package → transport: each step is completed before the next begins.
• Non-destructive first: photograph and sketch before lifting; collect fragile/transient evidence before robust items.

B. Search patterns

The pattern is chosen to guarantee total coverage without overlap.

1. Geometric patterns (open areas): strip/line (parallel sweeps), grid (two perpendicular strip searches, most thorough), and zone (area divided into sectors).
2. Point-based patterns (enclosed/central): spiral (inward or outward from a focal point) and wheel/ray (searchers move outward along radii from a centre).

C. Collection and packaging

• Individual packaging: each item in its own container to prevent cross-transfer; label with case number, item number, location, date, collector.
• Container by type: paper bags/envelopes for biological evidence (allow drying, prevent mould); airtight cans for arson accelerant samples; rigid boxes for firearms.
• Chain of custody form: signed at every transfer to preserve admissibility.

VI. Securing the Scene of Crime

Protecting the scene's integrity from the moment of discovery.

A. Establishing the perimeter

• Cordon: barrier tape or physical barriers mark the outer boundary; a single controlled entry/exit point is designated.
• Layered zones: an inner zone (evidence-rich core, minimal access), an outer zone (staging, equipment), and a public-exclusion zone.

B. Access control and preservation

• Entry log: every person entering records name, role, time in and out — deters unnecessary presence and documents potential contamination sources.
• Preservation: cover exposed evidence against rain or wind; do not smoke, eat, use the toilet or alter lighting within the scene.

VII. Documenting the Crime Scene

Creating a permanent, objective and reproducible record.

A. Purpose and the four methods

Documentation records the scene's condition as found, before anything is moved, so it can be reconstructed later and defended in court.

• Complementary record: notes, sketches, photographs and video overlap deliberately — no single method is complete.
• Objectivity: record facts and measurements, not opinions or conclusions.

B. Note making

Written notes are the running factual account kept from arrival onward.

• Content: date, time of arrival, weather, lighting, persons present, observations, and time of each action taken.
• Style: chronological, factual, legible and permanent (bound notebook, ink); no erasures — errors are struck through and initialled.
• Function: notes anchor the timeline and refresh memory for testimony months or years later.

C. Sketching

The sketch conveys accurate spatial relationships and distances that photographs distort.

• Rough sketch: drawn at the scene, not to scale, showing objects, measurements and a north arrow.
• Finished sketch: prepared later to scale from the rough sketch and measurements.
• Measurement methods: rectangular coordinates (distance from two fixed walls) and triangulation (distance from two fixed reference points to one object).
• Essential elements: title block, legend, scale, direction of north, case details.

D. Photography

Photographs give a true, detailed visual record of the scene and items in place.

• Three ranges: overall (whole scene and layout), mid-range (an item in relation to a fixed feature), and close-up (item detail, taken with and without a scale).
• Scale marker: an ABFO/L-scale in close-ups establishes true size.
• Photo log: each frame logged with number, subject, distance and orientation to preserve evidentiary value.
• Rule: photograph before anything is moved; alter nothing to "improve" a shot.

E. Videography

Video captures the scene's spatial continuity and context that stills cannot.

• Continuous walk-through: a slow, steady pass conveys the relationship of areas and the route between them.
• Constraints: no narration of opinions (only factual, minimal commentary or none), steady pace, adequate lighting, no bystanders in frame.
• Supplement, not substitute: video complements but never replaces still photographs and sketches, which give measurable detail.

VIII. Role of First Arriving Officer at Crime Scene

The initial responder whose actions decide the scene's evidentiary survival.

A. Immediate priorities

The first officer's early decisions have the greatest impact on evidence integrity.

• Safety and life first: render medical aid to the injured; if the scene must be disturbed to save life, note exactly what was moved.
• Assess and detain: determine if the offender is present; identify, separate and hold witnesses and suspects.
• Note conditions: record transient details — lights on/off, doors open, odours, time — that will change or vanish.

B. Protecting and handing over the scene

• Secure and cordon: establish the boundary, exclude unauthorised persons and begin the entry log.
• Preserve as found: avoid touching, moving or using anything; guard against contamination by responders and onlookers.
• Briefing: on arrival of investigators, hand over a full account of observations, actions taken, alterations made and persons present, transferring control of the scene.