Crime Scene Marking and Mapping, Part I

Crime scene mapping is vital for accurately defining the size and layout of a scene as well as the location of evidence.
This process traditionally relied on manual measuring techniques but is increasingly utilizing digital scanning devices.

Evidence marking is performed while searching the crime scene and is integral to the documentation of evidence.
Search methods include:
- Circle search
- Spiral search
- Line search
Common marking tools:
- Pre-marked placards (can be expensive)
- Homemade placards (e.g., folded index cards)
- Construction flags (preferred for visibility in photos)
Process for marking evidence:
- Upon encountering evidence, mark it immediately.
- Use a Sharpie to write a corresponding number on the placard or flag.
- Place the marker directly next to the evidence without disturbing it.
- Document the same corresponding number and a description of the evidence in an evidence log.

Evidence logs should include:
- Evidence number or letter
- Name of the finder
- Time and date of discovery
- Description of the item
Consistency in numbering (either all numbers or all letters) is crucial to avoid confusion in reports.

In all sketches, technicians document
- Size and layout of the scene
- Elements within the scene (furniture in interiors, landscape features in exteriors)
Fixing evidence allows precise placement of evidence within a scene.
- The choice of fixation methods may depend on scene severity and circumstances.
- Best practice involves always using the most precise methods regardless of the crime's severity.

Several methods exist for manual crime scene mapping:
- Rectangular coordinates
- Triangulation
- Baseline coordinates
- Polar coordinates
- Triangulation or rectangular coordinates on a grid
Important sequence:
- Photograph the scene prior to sketching and mapping.
- Fix all evidence before taking measurements of static items like walls and furniture.
- This sequence helps avoid inadvertently moving evidence.

Upon mapping the scene, important measurements include:
- Length, width, and height of all walls, doors, windows, and openings
- Specific locations of furniture and their dimensions
For flush items against walls, a single measurement can be taken from the item to a known reference point on the wall.
Differentiate between regularly shaped and irregularly shaped items for accurate measurement strategies.
- Regularly shaped: predictable shape, fixed using a minimum of four measurements.
- Irregularly shaped: no identifiable points, change shape when moved, fixed using measurements from the center of mass.

Best suited for crime scenes with clear boundaries (e.g., interior rooms).
Fast and effective, especially with measuring devices like lasers.
Process:
- Take measurements at right angles from the evidence to surrounding walls or surfaces.
- Generally requires two measurements from the center of mass of the evidence item.
- Less precise compared to triangulation due to reliance on limited measurements.
Example:
- Fixing a gun involves two measurements from its center to specific wall points.

Preferred and effective fixing method, emphasizing the regularity vs. irregularity of objects.
Regularly shaped items are measured using a minimum of four straight-line measurements from two landmarks creating two triangles.
Irregularly shaped items are fixed using measurements from the center of mass to landmarks, with overall item width being documented.
Landmark examples in triangulation:
- Base corners of walls
- Doors
Caution: Do not triangulate to or from items that are themselves fixed by triangulation.

When outdoors, use permanent objects (e.g., trees, rocks) as reference points.
- Avoid moving objects.
GPS use is limited at evidence sites; it does not provide the precision required for exact evidence locations.
- For precise and accurate evidence location, multiple measurements from distinct fixed points should be applied.
Three distinct fixed points provide an exact intersection for locating evidence items.
Remember, accuracy is crucial, and always emphasize the need for multiple measurements to ensure a detailed investigation is conducted.

Effectively mapping a crime scene and marking evidence is critical in forensic investigations.
Consistently using precise methods ensures a robust documentation process that aids in the investigation and potential trial outcomes.
Always prioritize thorough and accurate mapping, as it can significantly impact the integrity of the investigation.