Criminal Investigation Week 2
The Crime Scene Sketch


Quiz on reading assignment.

Lecture on sketches.  A common question is why we need a sketch if photographs are taken.  Sketches are used in all types of crime scenes to make sense of photo documentation and give prosecutors and others not familiar with the area a sense of the spatial distribution of crime scene elements (walls, furniture, evidence).  Photos have difficulty representing the distance between two objects in a photo, particularly when one object is close and other farther away.  This is a “depth of field” problem.  Photos can also distort relative or absolute size, which is often used by fishermen to make their catch look larger by holding the fish forward of their body.  Sketches are necessary because they sort out these spatial problems of photographs.  This is not to say that photographs are unnecessary—on the contrary, the job of the sketch is to make photographs more relevant and useful.

            The tools of sketching: Roll-a-tape, 100’ steel tape measure, graph paper, ruler (preferably an engineering ruler), drafting triangle (clear plastic triangle about 8” across), pencils, and crime scene template.  For large crime scenes, or where precise distances are not required (many minor traffic accidents), the investigator can pace off distances, but you must know the length of your stride.  Students should roll out a 100; tape and pace along the tape, counting their steps and dividing by the distance.  Aim to have a physical memory of your pace in an even number of feet in your stride so that multiplication is as accurate as possible under field conditions.

            Almost every crime scene can be measured by the 90 degree method.  Establish two straight lines at right angles and take measurements of items within the lines by measuring perpendicular to the straight lines.  If there are no easily found lines outdoors, such as a sidewalk curb or side of a building, you can establish a virtual line by running a string between two trees or other landmarks that are not likely to move.  Carefully document each end of the virtual line in your report so the line can be recreated in the future. 

            Record measurements carefully and use a measurement table to record distances from the two lines you have established.  Strive to make your sketch as close to scale as possible.  This is fairly easy with an engineering ruler or graph paper.  List the approximate scale in the legend of your sketch.  Every sketch, no matter how rough or simplistic, must have a legend.  The basic information in the legend is the location the sketch represents, the date, crime report number, and name of sketcher.  Some indication of north is also necessary.  Every piece of paper or electronic document involved in a criminal investigation must include a crime report number.  Imagine a records clerk who finds a document on the floor which came loose from its file.  Surrounded by thousands of files, and with no report number to connect the document to a case, a lazy clerk may just stick the document in a random file, causing all of your hard work to go to waste.  In this class, any lab report handed in without proper documentation will not be considered towards your score for that assignment. 

            Lab: Divide class into 2-person teams.  Assign to inside or outside crime scene which contains mock evidence.  Students will take measurements, complete a rough sketch, and then a finished sketch on the computer lab software. Students will be required to produce a paper sketch and an electronic sketch on software available in the computer lab.  100 points.

Reading Assignment for THIS week:

  Read and know these crime scene sketch handouts:

                Crime Scene Sketch,

                Crime Scene Diagramming,

                Measurement Table.

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           Christopher Bruno