Fingerprint evidence left at the scene of a crime can be of tremendous value to
an investigation because they are unique to every individual. When an offender
has been previously printed and leaves additional fingerprint evidence at a
second crime scene, this evidence can be used to positively identify that
particular individual as being at the scene of the crime or linking the two
cases.
There are two basic rules concerning fingerprints:
Fingerprints are unique to each individual, even identical twins have unique
ridge characteristics. There has never been a case where two individuals have
been found to have the same fingerprints.
Fingerprints are permanent. They are formed during fetal development and remain
unchanged throughout an individual’s lifetime.
There are three types of fingerprint evidence to be found at a crime scene:
Plastic: When an individual comes in contact with soft pliable surfaces
such as clay, wax, or grease, this will create a print impression in the contact
material.
Visable: When dirty hands come in contact with some substance and then
come in contact with a clean surface, they will leave a print on the surface
that is visible to the naked eye. Substances that will create a visible print
include blood, grease, dirt, or ink.
Latent: Prints may be created when the body’s natural secretions such as
perspiration and oils, are mixed with dirt or dust. Although these prints may be
left on a clean surface, they are not visible to the naked eye.
Prints can be “dusted” with powder and then “lifted” with tape and placed onto a
card. Different colors of powder can be used to find latent prints, and is
determined by the color of the surface to be dusted. A soft bristle brush is
used to lightly spread the powder, and if there are prints upon the surface, the
dust will adhere to them creating a contrast. The fingerprint will then need to
be lightly brushed further to create a distinct print. An alternative method of
dusting powder is made of magnetic material, which creates less mess, but cannot
be used on metal and is more expensive to use. Prints may also become visible
using the fumes of chemicals, which adhere to the print. Whatever material is
used, when the print is fully developed, it should be photographed before being
lifted with tape and being placed upon the print card for preservation.
Prints may sometimes become smudged, but leave a partial print that can be
identified or other trace evidence. In addition to fingerprints, palmer (palm or
wrist) and plantar (foot or toe) prints may also be used as evidence and are
collected in a similar fashion.
