How long do guns and bullets last

The bullet leads to the perpetrator

VDI nachrichten, Wiesbaden, September 5, 2008, sta - used casings and deformed projectiles often reveal more to murder investigators than alleged witnesses. The small metal parts bear the perpetrator's fingerprint - at least indirectly. They reveal many details about the weapon used. This greatly narrows the circle of suspects.

The clock shows after the first deep eclipse lies over Karlsruhe. Gravel crunches as a taxi stops in the parking lot of the waterworks. A man in a hoodie gets out and goes to the trunk. Driver Gabor R. follows him. Suddenly muzzle flashes through the night. Five shots tear the silence. Gabor R. sags to the floor. The perpetrator hastily dragged him into the nearby forest. Then he rushes back to the car and flees with the proceeds. The following afternoon a walker finds the body.

With a sure instinct, television commissioners would quickly name several suspects. Real investigators, on the other hand, have to work first: They cordon off the crime scene and secure evidence. Any fingerprints, DNA materials, hair or traces of blood are examined as well as textile fibers and remains of ammunition.

The firearms detection service of the Federal Criminal Police Office (BKA) in Wiesbaden is responsible for the projectile parts found. The authorities should use the metal parts to answer three questions: How many weapons were used? What type was it? And have the guns been used in another crime?

In the first step, the evidence ends up in the Forensic Science Institute (KTI). Anyone who suspects a laboratory made of glass and stainless steel in the style of the television series "CSI" will be disappointed. The clerks sit in simple, white plastered office rooms. One is wearing jeans and a checked shirt. He doesn't want to reveal his name. But he willingly lets you look over his shoulders.

“I first determine the caliber. Then I check the cases and projectiles under the stereo magnifying glass. ”At 25x magnification, he looks for grooves, notches and impressions. These arise, among other things, from the spiral-shaped trains in modern barrels (see box). “Each weapon model creates its own traces”, the professional knows with 19 years of professional experience. He quickly realized: "All shots were fired from a gun, caliber 7.65 mm Browning, with six fields and right-hand twist."

After a second look he adds: "The 0.7 mm to 1.1 mm wide field impressions on the projectiles as well as the traces of the firing pin, butt plate and the repeating action on the cases speak for a weapon from the former Yugoslavia." The data from of the approximately 8,500 specimens of the BKA's weapons collection confirm this thesis: The trace image exactly matches a pistol made by Crvena Zastava.

The question remains: has the weapon ever become conspicuous? Now something helps that cannot be seen in any crime thriller: the central crime ammunition collection. It contains ammunition parts from unexplained crimes in Germany.

The clerk purposefully reaches into a light gray cupboard. Projectiles that were fired with similar weapons are stored here in test tubes. The matching sleeves are right next to it, neatly inserted into foam mats. The “active part” of the collection currently contains around 5300 cases and almost 2000 bullets. Individual pieces only come into the “dead part” if the underlying case was more than 15 years ago. They will only be used at the express request of the investigators.

In a windowless laboratory, the expert now clamps a piece of ammunition from the taxi case and one from the collection under a comparative light microscope. At a magnification of up to 200 times, fine, µm-sized grooves within existing impressions become visible.

“It was only with the development of this device that ammunition parts could be examined,” explains the physicist Ruprecht Nennstiel, head of the “Firearms Detection, Ballistics and Weapon Technology” department at the CTI. "This makes it possible to prove whether two parts of ammunition come from the same weapon."

The view through the eyepiece shows the reflective brass surfaces of the two exhibits side by side, separated only by a vertical line. In order to find matches, the expert moves and rotates the illuminated objects in their respective holders. But in the end it says: No hit. A connection to previous acts cannot be drawn.

But Nennstiel discovers individual traces of the murder weapon. “The case bottoms have a peculiar shock bottom and firing pin impression. This could be due to a damaged firing pin. "

The ammunition parts from the taxi case go into the "active" collection. A few days later, an appraisal is sent to Soko. This has now evaluated over 400 reports - a decisive one was not included.

A few weeks after the taxi case, the clerk turned to three other cases and two projectiles. They come from Weinstadt near Stuttgart. A parked car was shot here. It soon became clear that the same weapon was used as in Karlsruhe.

In order to be able to quickly compare newly arrived cases and projectiles with ammunition that has already been registered, the BKA uses the "Evofinder" software. The program ejects the image files of potential hits after three to four minutes. The forensic scientist looks at them on a high-resolution 30-inch screen and examines individual areas of the trace. He places them next to each other, rotates and overlaps them and virtually changes the lighting.

The investigation team "Taxi" is immediately informed of the news. The new investigative approaches put the police on the right track: Exactly three months after Gabor R.'s murder, they arrested a 24-year-old. He owns a Crvena Zastava model 70 pistol, 7.65 mm Browning caliber.

The case does not end there. The seized weapon is now first sent to the CTI. A technician shoots her into a 4 m long pool of water. The aim is to obtain cases and projectiles with the weapon’s individual traces of fire without any further buildup or deformation. Then comes the ammunition handler's routine.

If the experts are still not sure, they use their sharpest sword: the comparison scanning electron microscope (V-SEM). The worldwide unique device consists of two coupled SEMs. In their vacuum test chambers, electron beams scan the objects in lines. At the same time, a detailed surface image of the respective evidence object is built up on the monitor with an extremely high depth of field. Trace areas of 20 µm can now be easily examined with 500-fold to 1000-fold magnification.

In this specific case, this method was not necessary. The imprints on the case showed that the seized pistol was used in both the murder and property damage.

The perpetrator's motive for murder was quickly found: he needed money to pursue his gambling addiction. He stole around € 250. That earned him a life sentence. The probability that the 24-year-old's crime would go unpunished was small from the start: the police currently solve over 95% of all homicides. B. GEHBAUER-SCHUMACHER

A contribution by:

  • Bettina Gehbauer-Schumacher