A cloud of microscopic gunshot residue particles released by firearm discharge. A typical gunshot residue particle of approx. 5 µm in diameter is shown in the upper left-hand corner.
Every shot from a firearm releases a cloud of microscopic particles which deposits in the surrounding environment – on both the shooter and the target as well. The identification of these gunshot residue particles and visualization of the distribution of this trace evidence may provide information about the distance between the weapon and the target, the direction of the shot and the type of deposition. Thus they provide important additional information that may be used to reconstruct the circumstances of a crime. The examination of gunshot residues on suspects’ hands, which indicate that a suspect has fired a weapon, is another important aspect.
Visualization of a gunshot residue distribution pattern with the aid of chemographical methods (above) and an X-ray fluorescence elemental mapping (below), using lead as indicative element (gunshot distance 5 cm).
Gunshot residue particles which adhere to exhibits or evidence material are identified analytically with the aid of several different instrumental methods and/or chemographic colouring. Scanning electron microscopy with X-ray microanalysis (SEM/EDX) is the most commonly used analytical method used to identify gunshot residue particles. Automatic particle detection systems developed specifically for this purpose help to distinguish between the large number of environmental particles not related to a firearm incident and gunshot residue particles. These are then classified according to their composition and examined manually by an expert for final confirmation.
In order to minimize the risk of evidence contamination, scanning electron microscope analysis is performed under clean-room conditions.
In order to minimize the potential risk of cross-contamination during these examinations, all investigations are performed under clean-room conditions. The clean-room is monitored continually to ensure the absence of contamination.
The KTI has made substantial contributions to significant innovations in the field of gunshot residue analysis in recent years. One major breakthrough was achieved through the modification of an X-ray fluorescence spectrometer, which is capable of scanning objects with large surface areas with spatial resolution.
Thus, in cases where conventional colouring is not applicable, it is now possible for the first time to visualize gunshot residue distribution patterns of elements for which no suitable chemographic agents are available.
Non-destructive examination of a gunshot damage with the Midex M X-ray fluorescence spectrometer.
Moreover, this method also provides a basis for the determination of muzzle-to-target distances in cases involving new types of ammunition with non-toxic primers.
Production of synthetic gunshot residue particles for use in international proficiency tests
Synthetic gunshot residue standards developed at the KTI have made a significant contribution within the context of international proficiency testing devoted to the improvement and harmonization of the capabilities of forensic laboratories worldwide. Today, many laboratories are using this patented fourth-generation reference material, which is also used to optimize and validate commercial electron scanning microscope/X-ray microanalysis systems.