The Crime Scene: Types, Securing and Documentation

Not every location connected to a crime is equal. Understanding the hierarchy of scenes shapes where resources go first and how thoroughly each location must be processed.

The primary scene is where the core criminal act occurred. In a homicide, it is typically where the victim was killed, which is often (but not always) where the body is found. In a burglary, it is the premises entered. The primary scene concentrates the largest quantity of physical evidence directly generated by the offence and receives priority in terms of resources, personnel, and documentation time.

A secondary scene is any associated location. A vehicle used to transport the body from the attack site to a dumpsite is a secondary scene; so is a suspect's home where bloodstained clothing was found; so is an ATM used with a stolen card after an assault. A complex case can have three or four secondary scenes, each requiring its own documentation and chain of custody, and each potentially carrying trace that the primary scene cannot provide.

The indoor/outdoor axis is a separate classification that affects method rather than priority. An indoor scene is bounded: air movement is limited, temperature is controlled, and access points are definable. An outdoor scene is open: weather changes it, animals interact with it, and the boundary is inherently harder to define. Outdoor scenes require a faster initial documentation pace because the window before significant environmental degradation is shorter.

The first officer to arrive at a scene is usually not a forensic specialist. They are a patrol officer, a constable, a first responder who is there because the call came in. What they do in the next ten minutes will either preserve or destroy the evidential record for the entire investigation. Their priorities are, in this order:

1. Check for life and render first aid
   Medical priority outweighs forensic priority. An injured person must receive care even if it disturbs the scene. When paramedics are present or needed, note exactly where they walked, what they touched, and what they moved. That log becomes part of the scene record.
2. Arrest or contain any suspect present
   An unsecured suspect is a safety threat and a flight risk. Detaining them also preserves trace evidence on their person: clothing, hands, and hair that forensic swabbing can exploit later.
3. Set the cordon
   Before any further action, establish a physical perimeter using tape, cones, or officers. Set it wide. The outer boundary can be pulled in once areas are cleared; it cannot be pushed out after contamination. Log the time the cordon was established.
4. Control access and start the scene log
   Every person who crosses the inner cordon must be recorded: name, role, time in, time out. This scene log is the foundation of the chain-of-custody narrative and will be scrutinised if the case goes to trial.
5. Preserve the scene until the specialist team arrives
   The first officer's job is to hold the line, not to investigate. No touching, no moving items to see them better, no walking routes that aren't pre-planned. If something must be touched (a door opened for access), note it immediately.

Setting the cordon correctly requires judgment. Too small and it is immediately compromised by responders, investigators, and onlookers; too large and it imposes unnecessary disruption, particularly in public spaces. The standard guidance in most forensic protocols is to set the boundary wider than instinct suggests and justify any reduction rather than any expansion.

A practical three-zone model is used in many jurisdictions, including the UK, Australia, India, and much of continental Europe. The inner cordon wraps the evidence area itself: only scene examiners with PPE enter here. The intermediate zone holds the scene commander, media briefing point, and any staging equipment. The outer cordon keeps the general public and press at a safe distance.

• Use a single controlled entry-exit point into the inner cordon. This means every entry is logged, contamination routes are minimised, and the perimeter is not compromised by multiple gaps.
• Establish a common approach path (CAP): a single route to the scene that all personnel use. If the CAP runs through an area of potential evidence, it must be documented and sampled before use.
• In outdoor scenes, account for weather when setting the perimeter. Rain or rising tide can move bloodstains and footwear marks within an hour. Priority sampling of exposed evidence precedes the standard documentation sequence.
• In high-density urban settings (a pub fight, a corridor assault), the practical boundary may feel absurdly large. Maintain it anyway. Evidence regularly extends further than the immediate event area: droplets travel, people flee, and items are discarded in motion.

Notes are the first documentation method and the only one recorded in parallel with events as they unfold. The scene log begun by the first responder is continued and expanded by the scene examiner, who creates a contemporaneous written record of every observation, action, and decision made at the scene.

What good scene notes contain: the time of arrival and the name of every person already present; a description of the scene as initially found, before anything changed; every item of potential evidence noted in place with its position described relative to fixed points; environmental conditions (lighting, temperature, weather, odours); any changes made to the scene and by whom; and the time of every significant action.

Notes serve a different purpose from photographs. Photographs capture appearance. Notes capture sequence, context, and the examiner's reasoning. When a blood trail leads from room A through a hallway to room B, the photograph shows it. The notes explain what the examiner inferred from the direction, the size of the drops, the absence of cast-off on the ceiling, and the decision to sample from specific points first. That reasoning record is what expert evidence in court is built from.

Crime scene photography follows a three-level protocol: overview, mid-range, and close-up. All three levels must be completed before anything is moved or sampled. Wide-angle and mid-range images that establish spatial context are frequently more valuable at trial than close-up images of individual items.

1. Overview (establishing) shots. Taken from outside the inner cordon, these show the whole scene, its relationship to the surrounding environment, and the approach route. Juries and judges who have never visited the location rely on these to understand the geography.
2. Mid-range (contextual) shots. Taken inside the scene, these show each item of evidence in relationship to its surroundings: a bloody shoe print relative to the door, a weapon relative to the body, a broken window relative to the room. They answer 'where exactly was it?' without magnification distorting scale.
3. Close-up (detailed) shots. Each item photographed first without a scale, then again with a scale marker placed beside it. The without-scale shot preserves the item's appearance in the natural scene; the with-scale shot enables measurement. Both are required, not one or the other.

Photography must be systematic and sequential. In a room, this means starting from one corner and working around the perimeter before moving inward, so that no area is accidentally skipped. A photographic log should record the frame number (or filename), what each image shows, and the direction of the shot. In digital photography, metadata (GPS, timestamp) is captured automatically, but should still be manually logged in case of device clock error.

A sketch is the only documentation method that records distances accurately. Camera lenses introduce perspective distortion that makes depth relationships unreliable for measurement. A scaled sketch, with measurements taken by tape measure, gives investigators and courts a spatial record independent of camera position or focal length.

The rough sketch is drawn at the scene, showing all fixed points (walls, doors, windows), evidence items marked with a number keyed to the evidence log, and measurements taken by triangulation or the rectangular coordinate method. North is marked. Scale is noted even if the rough sketch is not precisely to scale in execution. The finished sketch is produced later, either by hand on graph paper or using specialist software such as CAD or dedicated crime scene diagram tools.

Three common measurement methods are used depending on scene type. The rectangular coordinate method measures from two perpendicular reference walls, giving an X-Y coordinate for each item. The triangulation method measures from two fixed points that are not necessarily walls (useful outdoors), giving two radii that intersect at the item's location. The baseline method runs a measured tape along a central axis and records each item's perpendicular distance and distance along the axis, useful for linear scenes like corridors or roads.