Searching for shoeprints
Searching
for shoeprints on dark-colored
surfaces can be successful
if oblique lighting is used.
The shoeprints that may be present normally contrast well against
a dark background. Unfortunately, this technique is rarely useful
for light-colored surfaces, on which shoeprints contrast poorly
or not at all. If fingerprint powders are used
to find and visualize prints,
the fine details in a print may be damaged or
completely obscured. In the
worse case, the shoeprints are overlooked completely.
A
good technique to visualize
shoeprints on lighter floors
and other surfaces uses high-intensity
oblique lighting and a mirror.
Step 1
Position a mirror to stand
on the floor to be examined.
It should not stand upright
but lean backward at a slight angle
(see figure 1). The angle depends
on the distance between the
mirror and the point from which
you view the mirror. The closer you are to the mirror, the larger
the angle must be. For example, if you are 6 feet from the mirror,
its angle should be about 20 degrees from upright. At 12 feet,
the angle is about 10 degrees.
Step
2
Use a high-intensity light to create oblique illumination (search light, ALS,
or alternatively a slide projector). The path from the light-source to the mirror
must be diagonal, at an angle of about 30 degrees in relation to the mirror surface
(see figure 1). The shoeprints, if present, are now visible in the mirror. However,
your distance from the mirror and the angle of the mirror are crucial to the
result. Adjust these two factors until you get an image in the mirror that approximates
what you would see without the mirror if you laid your head on the floor.
Step 3
Once the traces are visible in
the mirror, they can be lifted. This will require that you move
toward the mirror. In doing so, you will note that the traces
you just saw in the mirror will
disappear. (As already mentioned, your distance from the mirror
and the mirror angle are of utmost importance.) To prepare for
this, use two laser pointers to indicate the shoeprint on
the floor. Place one in the center of the toe of the shoe
and one in the center of the heel (see image 1). Aim with
the laser pointers on the floor in front of the mirror, and
follow the movement of the dot while looking at the mirror.
At
this point you know exactly
where the print is located, and you can lift it with a black
Gellifter. Holding the Gellifter by its two short ends, plan
to apply it so that the center-point
of each end covers one of the laser dots (see image 2). Apply
one end first, and then work toward the other. We recommend
using a rubber roller to avoid any air bubbles.
Step 4
The shoeprint is now lifted and
can be taken to the lab for photography and further examination.
Image 3 shows the actual color of the floor from which the sample
print was.
For
more information go to BVDA
at the following Web site: http://www.bvda.com/EN/prdctinf/en_mirror_technique.html
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