How does Luminol help solve crimes?
By Deepshikha Khosla
Cop shows and movies show you an unbelievable range of gizmos
that can perform unimaginable tasks ¨C such as bringing into focus
a single voice from an otherwise muffled recording or computers
that can zoom in on a tiny section of the image on the screen. Most
of it is pure fiction. But one seemingly strange chemical that glows
when it comes into contact with blood is for real. It¡¯s called
Luminol is a chemical that glows with a bluish light when it comes
in contact with blood. It even reacts with years old traces of blood.
An ultra-sensitive chemical, it can detect blood at one part per
million. In simple language, this means that if there is even one
drop of blood in 999,999 drops of water, luminol will glow. Hence,
extensively used for criminal investigations, luminol has helped
crack some pretty tricky cases of detection.
Victims of bloody, violent crimes cannot disappear without a trace ¨C
that is the basic assumption on which crime scene investigators
function. No matter how hard the murderer tries to clean up the
blood and dispose of the body, some tell-tale traces of blood will
remain. Tiny blood particles can cling to most surfaces for years on
end, without ever being seen.
Luminol is effective in revealing these traces. There is a chemical
reaction between several chemicals and hemoglobin (a protein in
the blood that carries oxygen), that produces light. There is a
breakdown of molecules, which then rearrange themselves to form
different molecules. In the chemical reaction of luminol, the original
molecules (reactants) have more energy than the new molecules
(products). The extra light is discarded by the molecules in the form
of light photons. This phenomenon is known as
Luminol is typically used at a crime scene where bloodshed is
suspected to have happened but no traces of blood are visible to
the naked eye. The room is darkened and then the chemical is
sprayed over a large area. If blood traces are revealed, then
investigators videotape or photograph the crime scene.
The tricky thing about luminol is that substances (such as
household bleach) other than blood may also cause luminol to
glow. Hence, a glow merely reveals to investigators the possibility
of blood in the area. An experienced investigator, by observing the
speed of the chemical reaction can judge whether the substance
was blood or something else. But in order to be absolutely sure
that it was blood, other tests need to be run.
Luminol helps to provide clues as to how events may have
unfolded or the kind of weapon used. For example, blood splatter
patterns of a blunt object versus those of a sharp knife will be
different. Sometimes, bloody shoe prints give a lot of clues about
the movements of the assailant after the attack. Luminol may also
lead investigators to discover new evidence. For instance, if there
is a positive reaction to luminol sprayed on a carpet, then removing
the rug may reveal blood-soaked floorboards.
Despite being a key investigative tool, luminol has one
disadvantage ¨C the chemical reaction can destroy other evidence
in the crime scene. Hence, contrary to what a layman might think,
luminol is only used after other extensive investigations have failed
to reveal enough clues.
About the Author
How does law enforcement use Luminol to solve crimes? Find out at http://www.crimjustice.us
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