Fingerprints
Fingerprints are one of the most important
things that link a suspect with a
crime scene. Even though that fingerprints
are not always left by a criminal,
the crime scene should still be examined
for them. All people have distinct
friction ridges on the skin of the
fingers. In leaving an impression, an outline
of the ridges is transferred
and duplicated by oil, sweat and other substances
on the object handled. The
impression is usually not visible. Fingerprints not
visible are called latent
prints; so something must be done to make them
visible. The most common way
to make them visible is to "dust" an
object with fingerprint powder. The
color of the powder should contrast with the
surface, such as black powder on
light-colored backgrounds and white powder on
dark. An alternative to using
powders, is using chemicals. The most common to
use are Iodine, ninhydrin,
silver nitrate, or cyanoacrylate esters. The process
involves fuming,
spraying, brushing, or dipping the object in a solution of the
chemical. Yet
another way to make fingerprints visible is to use radiation.
There are
two kinds of radiation to use, Ultraviolet rays, and laser radiation.
A
latent print requires a suitable surface for it to be picked up.
Porous
surfaces such as unpainted wood and some kinds of paper are unlikely
to yield a
useful impression. Smooth surfaces like glass, enamel, and glossy
paper are
ideal to lift the print if you are lucky enough to get it.