How Does Luminol Work?
© 2017 - Stephanie Hoover, All Rights Reserved
You're watching your favorite crime scene investigation show. It's the point in the story where the suspect has been led away in handcuffs. The oddly-coiffed crime tech hurries into the perp's bedroom. She pulls a small spray bottle from her lab coat pocket. She pumps the top once or twice and, within seconds, the entire wall glows a brilliant blue. She casts a knowing glance at the detective who declares, "It was a bloodbath in here." The camera zooms in on the real star of the scene: the bottle of luminol, still in the crime scene tech's capable, gloved hand.
While this scenario may play well in the fictional world of crime TV, true forensics experts know it's malarky. Does luminol detect blood? Of course. Does it immediately signify whose blood? Not a chance. And what about that blue glow? Well, maybe the suspect was a heavy cigar smoker. Or really liked horseradish.
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As everyone reading this article knows, luminol exhibits what the scientists call "chemiluminescence." That's a fancy way of saying that it glows blue when reacting to hemoglobin and other substances.
Reportedly first synthesized in 1902, it was not until 1928 that a German chemist first studied and recorded luminol's peculiar reaction to blood. Another German, forensic scientist Walter Sprecht, first tested it at crime scenes in 1937.
According to a document created by the National Criminal Justice Referral Service, luminol was first proposed for American forensic applications in 1942. It took some time for police departments to accept - not to mention understand and afford - luminol and its attendant training and equipment requirements.
The first widely reported use of luminol in this country was in 1954 during the murder trial of Dr. Sam Sheppard. Henry Dombrowski, a lab employee in Cleveland's scientific identification bureau, was known as a "blacklight man." He testified about his use of luminol during the Sheppard investigation and his subsequent findings indicating blood in the bedroom.
Challenges to luminol evidence were, and are, numerous and sometimes quite valid. Common household items like bleach can trigger false positives, as can vegetables like the aforementioned horse - and other - radishes, turnips, carrots and even green beans. Residue from heavy cigarette and cigar smoke can affect results, as can the presence of varnish or oil-based paint.
A misconception oft-perpetrated by Hollywood involves the level of intensity of luminol's glow. Although cop shows would have us believe that a brighter blue equates to larger quantities of blood, in actuality it typically indicates the age of that blood. Older blood produces more chemiluminescence.
Luminol, by the early 1990s, became a standard tool for forensics teams in even small police departments. It is, unquestionably, the most reliable indicator of the presence of blood. Early luminol adopter and forensics expert Gary A. Rini famously promised it can indicate one drop of blood in five million drops of water.
What luminol can't do is immediately identify the victim or killer, nor can it solve every crime on every television network - or in real life, for that matter.
Want to test it for yourself? Contrary to popular belief, luminol sales are not restricted to law enforcement personnel. In fact, you can buy it online for less that the cost of a good lunch for two.
Lab coats sold separately. ☁