Criminal Investigations Crime Scene Diagrams

Learning Goals: Understand the importance of diagrams. Know the two methods of measuring objects at a scene. Perform measurements and complete a diagram of a scene.

Crime Scene Diagrams Done for serious crime scenes and major accidents. Augments pictures and notes / reports. Simple, clean, line drawings that indicate the positions of evidentiary objects in relationship to fixed objects at a scene. Diagrams allow for measurements (unlike pictures).

Crime Scene Diagrams Excellent visual aid which selectively includes significant objects and leaves out unnecessary details. Will clarify the appearance of the scene and make it easier to comprehend. Admissible in court and are often used in big blow-up charts.

Crime Scene Diagrams Photographs may not be enough to sufficiently record a scene. Photographs create a different perspective and do not always depict the exact location of objects or their relationship to each other. Photographs do not show measurements or true distances. Photographs may have distortions.

Crime Scene Diagrams Refresh the memory of the investigator. Refresh memory of the witnesses. Refresh the memory of the cooperative suspect (who may assist with further details regarding the scene). Develops a clear understanding of events.

Crime Scene Diagrams More descriptive than hundreds of words. Can show sequence of events. Can show trails and patterns of movement.

General Rules for Diagramming Show all objects that have a bearing on the crime scene. Locations of entrances / exits. Show which way the door opens / direction of swing. Location of weapons / evidence relative to the victim and stationary objects. Windows.

Methods of Measuring Rectangular Coordinate (Baseline Method) Used indoors. Use a baseline that is fixed and permanent (wall). Measure items using a 90 degree angle from the baseline.

Methods of Measuring Triangulation Method (creation of a triangle of known distances) Primarily used for outdoors. Used two fixed points of reference. Measures the object from the two fixed points. (which creates the triangle) Can have any degree of angle. May have to establish a secondary fixed point. (drive a spike into the ground)

Methods of Diagramming Overview Projection (most common)

Methods of Diagramming Cross Projection (Used to gain three dimensional perspective

Items to be Measured Measure at least 2 points on an object to be able to properly place that object back into a scene. A human body will need at least 6 points of reference to be placed back into a scene (head, hands, feet, torso)

Items to be Measured Depends on the object measured. On a tool or small item, measure to the edges or points. On a body, measure to the center mass of a particular body part.

Three Types of Sketching Sketch of Locality (gives a picture of the crime scene and it’s environment, i.e. neighboring buildings and roads) Sketch of Grounds (gives a picture of the scene with it’s surroundings, i.e. a house with it’s property outlined, an office within an entire floor plan)

Three Types of Sketching Sketch of Details (description of crime scene within it’s immediate surroundings, i.e. the room in which the crime was committed)

Diagrams Should Include: Case number. Address or location descriptor. Date/Time. Officer name/serial number. Type of offense. Victim’s name. Entrances/exits/windows.

Diagrams Should Include: Size of scene. Indicate north with “N” Show all measurements. Include a key or legend. Include a disclaimer of “not to scale” unless working with precision instruments.

Diagrams May be performed by patrol officers on collision investigations, natural death investigations, and/or other cases that need it or where someone requested to have it.

Finished Diagram on Graph Paper

Diagrams on Graph Paper Easier to do on graph. Provides guidelines for line measurements.

Diagrams On major crimes and major collision scenes, diagrams will likely be done with computer assisted drawing (C.A.D.) programs.

Drawing in 3D Height Width Depth

Technological Advances Computer Aided Drawings (C.A.D.) Global-Position Satellite Devices (G.P.S.) Total Station (laser guided measurements)

Total Stations

Laser Measurements Similar to a total station.

3D Scene Digitizer Costly to buy. ($44,900) Sets up on tripod. Measures room up to 40 ft.

3D Scene Digitizer Can create a “wire-frame mesh”. (3D model of a scene)

Technological Advances Reasons why advanced tools are not in use: Prohibitive costs. Time to train. Tech overload. Prediction: Hand-held or portable devices will measure and diagram scenes quickly and efficiently and lessen a detective’s workload. Pen and paper will be done away with and a machine will do the drawing of scenes.

Artist’s sketch of scene Shows detail Eliminates obscurity Sketch artists can replicate the scene and clear up some of the details that appear obscured in photos.

Things to Remember: Decide what is to be sketched beforehand. Don’t sketch until familiar with the scene. Leave out objects not relevant to the case. Include only essential information.

Things to Remember: Your diagrams will not be exact, they will be approximate. Rough sketch to be included with the case file as well as the finished copy.

Errors when Diagramming: Measuring a distance by pacing and then recording results in feet and inches. Relying on memory alone. Correctly outlining the dimensions of a room and then placing objects within by mere visual means (no measurements). Not being able to read your measurements. Improper measuring device or technique.

Practical Exercise Practice measuring objects within the classroom using the methods given in class.