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:
Back to Criminal Investigation
© Christopher Bruno