by Andrea Campbell
I
am never surprised at the results that can be achieved with forensic
science. It is comforting to know that as time moves on, so do
improvements in evidence collection and evaluation. Today’s story
illustrates these ideas and even though it happened in Sweden, we are happy to see a righteous outcome.
High-Intensity UV Lamps
Body
fluids are an important part of a crime scene, in murder and especially
with sexually-based crimes. Since body fluids have properties that make
them fluoresce under alternate light, it makes sense to walk the scene
carefully with the light in hand and mark all the stains with cones or
markers that may prove to be clues later on. The light won’t tell you what you’re looking at, but after collection and examination, you may get DNA and other readings.
The Rape in Sweden
On a cold day in Sweden, crime scene investigator Birgitta Jansson, who is with the Karlstad, Sweden police
technical division, walked through the snow. It was dawn at about 7:20
in the morning and the sun was waiting to rise over the horizon. An
outdoor scene, the crime was committed in a residential area near the
center of town, and not far from a school. The case was an alleged rape
and it took place at the corner of a hockey rink in a snow drift.
The
snow left behind some obvious impressions: the shape of a human
figure—arms, legs and torso—that were clear enough. In addition to the
visual evidence were some Swedish coins that had fallen from the
perpetrator’s pockets that were lodged deep in the snow. Blood was also
found near the coins, and all were subsequently collected as evidence.
Investigators then used a high-intensity ultraviolet light
to illuminate the scene, just as the sun was beginning to rise. Three
spots, thought to be semen, were found in a 4 x 4-inch area.
“The
light made the semen fluoresce in the snow, to the extent that I never
thought possible,” said Jansson. “Actually, I was amazed that it worked.
I never thought you could distinguish semen from snow with the help of a
high-intensity UV light. And there was no doubt—the fluorescence was
incredibly strong and clear. I have never seen anything like it.”
Jansson
examined the glowing pieces more closely and found that they were now
frozen liquid laying separate from the snow. They secured and collected
those lumps of ice and packed them into bio bags, stored them in the
freezer in the police car, in the hopes of sending the frozen liquid to
the laboratory.
Back at the Laboratory
Once
the lab examined the frozen, cube-like evidence it was clear that there
were both semen and vaginal secretions. The sperm produced DNA and was
ultimately matched to the vaginal swabs taken from the victim. The
rapist was subsequently tried, convicted and sentenced.
Semen,
vaginal secretions, urine, sweat and saliva are all bodily fluids that
will fluoresce under UV light. Urine is the easiest to detect, followed
by semen, and the others will too, only more often very faintly.
Rehn, Lisel, “Semen fluoresced in the snow solved a rape case in Sweden,” Evidence Technology Magazine, July-August 2011, pp 24-25.
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2 comments:
Amazing how "evidence" has changed.
Ann
How en-'lightening'!! TNX
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