Sketching and Diagramming for Forensic Evidence

Sketching

• Sketch definition (Meriam-Webster): a rough drawing representing the chief features of an object or scene, often made as a preliminary study.

• Portrays information accurately and not necessarily artistically

• Aids in reconstruction

• Aids in interviews

• Displays proper proportions and relationships

• Makes permanent record of conditions not easily recorded

• Purposes and use

  • Supplements written reports and photographs

  • Simple drawing showing items of physical evidence in relation to each other and reference points

  • Can be used to refresh memory

  • Can be used in court

• Practical expectations

  • Doesn’t have to be perfect, but it should be representative

  • Neat enough for someone else to understand it in the future if you are not around

Diagramming

• Diagramming definition: A drawing that shows arrangements and relationships. It is a formalization of your sketch used for trial and reconstruction. Diagrams may be to scale or not to scale and can be CAD-assisted or hand drawn.

Measuring Methods

• Two main approaches

  • Consecutive: each measurement inline is taken from the last measured point

  • Example: $10' \rightarrow 5' \rightarrow 8'$

  • Cumulative: all measurements inline are taken from a common point of origin

  • Example: $10' \rightarrow 15' \rightarrow 23'$

• Documentation practices

  • Use a separate measurement log to record measurements unless there are only a small number of items

  • The only measurements that should be in the sketch/diagram area are the room dimensions unless it is a very small scene

Basic Equipment

• Graph paper

• Pencil & Eraser

• Ruler/straight edge

• Clip board

• Tape measures (metal, fiberglass, cloth)

Advanced Equipment

• Laser

• Sonic

• Wheel

• Total Station

• 3D Laser Scanner

Diagram Elements

• Heading

• Legend

• Title Block

• Scale and Direction

• Sketch/Diagram Area

Heading

• What is its purpose?

• Is it a sketch or diagram (rough sketch)?

• Is it a part of a larger diagrammed area?

Legend

• Defines symbols used to include numbers and letters

• Do not assume someone knows what a symbol you used means

• Keep it clean; don’t overcomplicate

• Keep numbers and letters consistent with notes and photographs

• Use symbols or letters/numbers, NOT BOTH

Title Block

• Location

• Case number/name

• Who completed the diagram/sketch

• Who took measurements

• Date of creation

• To scale or not

Scale

• Is the diagram to scale?

  • Not a precise scale

  • If it is to scale, include an accurate scale

  • Do not use $1' \text{ }= \text{ }1'$ because it will not be accurate if blown up for court, etc.

Direction

• Directional arrow usually pointing North

• Appropriate for the diagram

Sketch/Diagram Area

• Do not over clutter

• You do not have to include every item if it does not have any evidentiary value (even if it is to scale)

• Do not use symbols and labels for the same item

• Take your time and make your sketch understandable by others; someone may have to create a diagram from your sketch years later

Methods of Measuring

• Common methods include:

  • Triangulation (most common)

  • Rectangular Coordinate (most common)

  • Baseline Coordinate

  • Polar Coordinate

  • Total Station / 3D Scanner

• Additional notes

  • Measurements are usually taken to the center of the object

  • If orientation is pertinent to the investigation, multiple measurements may be needed

  • Determine if the third dimension is important

Triangulation

• Uses two fixed reference points

• Record distance between reference points

• Record measurements from both fixed points to the object (±/−)

• Add to the diagram using a compass to scribe arcs or a computer program

Rectangular Coordinate

• Uses two measurements taken at right angles from the object being measured

  • Example: East/West and North/South to the walls of a room

• Can employ a 0,0 origin and reference all measurements to this zero

Baseline Coordinate

• Uses a datum point to fix a baseline

  • Datum is normally located by triangulation or GPS coordinates in large outdoor scenes

• The baseline then extends from the datum in a cardinal direction

• Two measurements are taken:

  • Down the baseline

  • 90 degrees from the baseline to the object (±) or East/West

Polar Coordinate

• A large azimuth ring is oriented north and secured to the ground so it can’t rotate

• A measurement is taken from the center of the ring to the item and then degrees from 0 are recorded

• Best used for large outdoor areas

• Equipment:

  • Large compass rose/azimuth ring

  • Compass for orientating the ring

  • Long tape measure

Total Station / 3D Scanner

• Uses lasers to measure distances and angles to objects

• Uses a form of the Polar Coordinate method

• Data can be imported directly into mapping/diagramming software

The Crime Scene Sketch

• Most diagrams are created using an orthographic view (Bird’s Eye)

• Different views may be employed if evidence with elevation is recorded

• Special types of diagrams:

  • Cross-projection/Exploded view

  • Elevation view

  • Three-Dimensional view

Cross-Projection / Exploded View

• Used to show items of evidence with elevation

• Walls and ceiling laid out flat as necessary on the same plane as the floor

Elevation View

• Used to show items of evidence with elevation

• Usually used to document evidence on walls

• Measurements taken 90 degrees to floor

• Measurements can be taken using Rectangular Coordinate method or Baseline Coordinate method, modified by using the floor of the wall as the base line

Three-Dimensional View

• Uses perspective to show items of evidence with elevation within the scene

• Harder to make without computer software programs

Examples and Case Details (Illustrative)

• Example: Crowbar

  • LEGEND, NORTH arrow, SCALE: 3/8 Inch = 1 Foot

  • TITLE BLOCK includes:

  • CASE NUMBER: 1426-82-CT0063

  • SCENE PORTRAYED: Room 7, Bldg As-3253-* Troop Billets

  • LOCATION: Ft McClellan, AL 36205

  • OFFENSE: Burglary investigation

  • VICTIM: SPS Betty H. Holmes

  • TIME DATE BECAS: 1030, 12 Jan 82

  • SKETCHED BY: Hr. Frank L. Wright

  • VERIFIED BY: SA David L. Kelly

• Example: Marina’s Bath Elevation

  • SCALE: 0'-1/2" = 1'-0"

Three-Dimensional Software Example

• Autodesk Revit© example

• Demonstrates a 3D view workflow (Dundalk Institute of Technology project)

General Notes

• Most diagrams are orthographic views, but alternative views are used when elevations or complex perspectives are needed

• Practice with Cross-projection, Elevation, and 3D views to accurately communicate the scene

• The lab/review sections indicate practice material and assessment preparation