Semen fluoresced in the snow solved a rape case
Written by Lisel Rehn   

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THE SCENE where the rape took place was covered with an inch of fresh snow. It was dawn, 7:20 a.m., and the sun was about to



Crime-scene investigator Birgitta Jansson of the Karlstad, Sweden, police technical division had been called to the scene. The crime scene was outdoors, in a residential area not far from a school, near the center of town. The rape took place in a snowdrift, at the corner of a hockey rink.

“The crime scene was very obvious, as we found clear evidence of a human figure shaped in the snow—showing arms, legs, and torso,” said Jansson. “We found a collection of Swedish coins, as well, pressed deep into the snow. The position of the coins indicated they slipped out of a pocket and then were buried into the snow. A red fluid next to the coins, suspected to be blood, was secured.”

In spite of the fact that the sun was beginning to rise, investigators used a high-intensity ultraviolet (UV) light to illuminate the crime scene. Three fluorescent spots were found in a 10 x 10 cm (4 x 4 in.)area.

“The light made the semen fluoresce in the snow, to an extent that I never thought was possible,” said Jansson. “Actually, I was amazed that it worked. I never thought that you could distinguish semen from the snow with the help of high-intensity UV light. And there was no doubt—the fluorescence was incredibly strong and clear. I have never seen anything like it.”

On further examination, Jansson discovered that the fluorescing spots were actually frozen liquid in the snow.

“We secured the lumps of ice by breaking loose the snow and packed them into bio-pack bags and stored them in the freezer in the police car,” said Jansson. “After melting the frozen liquid and securing it, it was sent off to the laboratory.”

The laboratory results showed DNA from sperm as well as vaginal secretions—all taken from the fluorescent ice cube. DNA from the sperm in the fluorescent ice cube matched the sperm found in vaginal swabs from the victim.

The rapist was subsequently tried, convicted, and sentenced.

This is a closeup of the rape scene.
You can see impressions of the victim's head, arms, and torso.
Drops of blood are also visible.

The crime-scene investigators
used a high-intensity ultraviolet (UV) light
to illuminate the scene.
The fluorescent spots proved to be semen.

High-Intensity UV Lamps

Most stains from body fluids have some fluorescent nature and can be seen when using a high-intensity UV light. In most cases, it is not possible to see such stains otherwise.

The most effective way of using the UV lamp is to use it to “mark” the crime scene. In other words, you survey the scene with the UV lamp and mark all stains that could be useful traces. When using an intense UV light, it is also possible to see things fluorescing at a distance that otherwise would be impossible to see.

While the UV light cannot confirm exactly what sort of stain you are looking at, it does indicate where the stains or body fluids are. This makes it possible to then take samples or perform further investigation.

What body fluids are
fluorescent by nature?

  • Semen—Semen is very fluorescent by nature and the fluorescence can be observed on dark as well as light textiles when illuminated with an intense UV light, without the need for using colored goggles.
  • Vaginal secretion—Vaginal fluid is very difficult to detect at all times, as it has a very weak fluorescence.
  • Urine—Urine is easy to detect, as it is very fluorescent when illuminated with ultraviolet light. You can even see it at great distances. Finding urine can be valuable as it can be analyzed for traces of blood or other particles that contain DNA.
  • Sweat—Sweat contains DNA and is usually easy to see with high-intensity UV light.
  • Saliva—Saliva contains DNA and is fluorescent with UV light.

About the Author

This e-mail address is being protected from spam bots, you need JavaScript enabled to view it is the managing director at Labino, a company that develops, manufactures, and sells UV lamps.

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