The purpose of crime scene investigation is to help establish what happened (crime scene reconstruction) and to identify the responsible person. This is done by carefully documenting the conditions at a crime scene and recognizing all relevant physical evidence. The ability to recognize and properly collect physical evidence is oftentimes critical to both solving and prosecuting violent crimes.
The major assignments, as well as corresponding general duties and responsibilities, are set forth as follows:
Trace evidence is based on Locard’s Exchange Principle which contends that every contact, no matter how slight, will leave a trace. The trace is normally caused by objects or substances contacting one another, and leaving a minute sample on the contact surfaces.
The main point is that some apparently foreign object or piece of material has been brought to a crime scene and tracing its origin can assist in an arrest and conviction. Similarly, finding some trace from the victim or crime scene on a suspect can also have a strong impact on a case.
SKETCHING THE SCENE
The Photograph is ordinarily a two-dimensional representation of the scene of the crime and, as such, does not provide accurate information concerning the distance between various points in the scene. The relationship existing between objects present in the scene cannot be clearly understood unless the measured distances are known. Certain objects, moreover, are not visible in a photograph or cannot be clearly identified. A drawing or crime scene sketch is the simplest and most effective way of showing actual measurements and of identifying significant items of evidence in their locations at the scene. Sketches are divided generally into rough sketches and finished drawings.
Rough Sketch. The rough sketch is made by the investigator on the scene. It need not be drawn to scale, but the proportions should be approximated and the appropriate measurements or dimensions shown. The rough sketch may be used as a basis for the finished drawing. No Changes should be made on the original sketch after the investigator has left the scene.
Finished Drawing. The finished drawing is made primarily for courtroom presentation. It is generally based on the rough and drawn to scale by a person skilled in either mechanical or architectural drawing