LOCATING EVIDENCE ON SKETCHES
Various sketch methods may be used to locate evidence and other important items at the scene. The
simplest form of a sketch is a two-dimensional presentation of a scene as viewed directly from above. Evidence
is located on this type of sketch by triangulation. Triangulation is used for indoor and outdoor sketches having
fixed reference points. Objects are located by creating a triangle of measurements from a single, specific,
identifiable point on an object to two fixed points, all on the same plane, at the scene. If movable items are to be
used as reference points, they must first be "fixed" themselves. Do not triangulate evidence to evidence. Do not
triangulate under or through evidence. Do not take a line of measurement through space. Measure your line
along a solid surface like a floor, wall, or table top. In the interest of clarity, keep the angle of triangulation
measurements between 45 and 90 degrees on the sketches.
Regular shape items are fixed by creating two separate triangles of measurements. Each originates at
opposite points on the object and ends at two fixed points, on the same plane, at the scene. This is commonly
known as the 2-V method of triangulation.
Pliable objects are fixed by creating a single triangle of measurements from the center of mass of the object
to two fixed points, on the same plane, at the scene. You also measure the longest and widest dimensions of the
object.
Inhabited outdoor areas usually have easily defined, fixed reference points, such as buildings, edges of
roads, and sidewalks. When these are present, the triangulation method can be used to establish the location of
objects. But uninhabited or remote areas may not have easily defined, fixed points within close range. In such
cases, objects will have to be located by using the intersection-resection method taught in map reading.
Cross-projection is used to add another dimension to sketches. The added dimension is useful when items
or locations of interest are on or in wall surfaces in an enclosed space. The walls, windows, and doors in a cross-
projection sketch are drawn as though the walls had been folded out flat on the floor. The required measurements
and triangulation of evidence are then entered on the sketch. A cross-projection drawing may be used as a scaled
drawing.
Figure 2-2 depicts an example of a rough sketch of an interior crime scene showing evidence measurements and
triangulation. See Figure 2-2.
Figure 2-3 depicts an example of a rough sketch of an outdoor crime scene showing evidence measurements and
triangulation. See Figure 2-3.
Figure 2-4 depicts an example of a finished sketch drawn to scale of an indoor crime scene. See Figure 2-4.
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MP2002
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