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BACKGROUND: The in situ classification of bullets is of interest in forensic investigations when the bullet cannot be removed. Although computed tomography (CT) is usually performed on shooting victims, visual assessment, or caliber measurements using CT can be challenging or infeasible if the bullets are deformed or fragmented. Independent from the bullet's intactness, x-ray attenuation values (CT numbers) may provide information regarding the material of the bullet. METHODS: Ethical approval was not required (animal cadavers) or waived by the ethics committee (decedents). Copper and lead bullets were fired into animal cadavers, which then underwent CT scanning at four energy levels (80, 100, 120, and 140 kVp). CT numbers were measured within regions of interest (ROIs). In addition to comparing CT numbers, the dual-energy index (DEI), representing the ratio between the CT numbers of two energy levels, was calculated. The most appropriate method was applied for decedents with fatal gunshot wounds. RESULTS: CT numbers demonstrated no significant difference between copper and lead bullets, and false classifications can easily occur. DEI calculations revealed significant differences between the two groups of bullets. The 120/140 DEIs calculated from the maximum CT numbers obtained from ROIs at the edge of copper versus lead bullets presented a significant difference (p = 0.002) and a gap between the CT numbers of copper and lead bullets and was successfully applied for the decedents. CONCLUSIONS: This study presents a viable method for distinguishing copper and lead bullets in situ via CT and highlights the potential pitfalls of incorrect classifications.

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Computed tomography (CT) scans of gunshot wounds and their high sensitivity in detecting osseous lesions has often been reported in the literature. However, studies concerning in situ examinations of lodged projectiles with CT to determine the ammunition used are lacking. Projectile visualizations are hampered in standard CT due to the presence of metal artifacts and the limited range of Hounsfield units (HU). The use of special reconstruction algorithms can overcome these limitations. For instance, using extended CT scale (ECTS) reconstruction supports detailed visualizations of metallic objects. In addition to projectile visualizations, X-ray attenuation measurements (CT numbers) of metallic objects can be used to differentiate materials in CT. This study uses real forensic cases to demonstrate that-depending on the degree of deformation-a detailed visualization of lodged projectiles using ECTS can provide useful information regarding the ammunition used and allows accurate caliber measurements. Independent from the degree of deformation, the in situ classification of bullets, even fragmented bullets, according to their metallic components is feasible by dual-energy index (DEI) calculations. The assessment of a lodged projectile with CT images provides useful information on the case; thus, a close examination of lodged projectiles or bullet fragments should be a part of the overall radiological examination for cases of penetrating gunshot wounds.

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The aim of this study was to compare three gunshot residue (GSR) collection methods used in conjunction with chemographic detection applied by different regional Swiss police services. The specimens were collected from the hands of a shooter with either filter paper (Filter method) or adhesive foil. The adhesive foil was then either applied against photographic paper during visualisation (AF Photo method) or coated with a layer of polyvinyl alcohol (AF PVAL method). The experiments involved two conditions of the examined hands, i.e. dry and humidified. The residues were revealed using the sodium rhodizonate test (SRT). Preliminary tests assessing the possibility of conducting a confirmatory Scanning Electron Microscopy coupled to Energy Dispersive X-ray spectroscopy (SEM/EDX) analysis after the chemographic test were performed on a number of specimens by cutting positive spots and mounting them on stubs. Obtained results were compared in terms of effectiveness - number of positive spots, time requirements, quality of subsequent SEM-EDX analysis, ease of use and cost. The Filter method generally yielded a high-quality detection with both dry and humidified hands, as well as a simple, quick and efficient confirmation by SEM/EDX. The AF Photo performed well on dry hands, but not on humidified hands. The AF PVAL method performance was lower compared to the other methods in both examined conditions of the hands. The SEM/EDX analysis showed that the Filter and AF PVAL method provided satisfactory results when a sufficient carbon coating thickness was applied to the cuttings. It was also observed that the thinner the PVAL layer, the better the quality of the spectra and obtained images in SEM/EDX. Furthermore, the surface of the photographic paper did not seem to be conductive, even after the application of a thick layer of carbon. In conclusion, the Filter method gave the best overall results, but its application required slightly more time and expertise than the two other methods.

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OBJECTIVE. This study aimed to identify bullets on the basis of their metallic components and to distinguish between ferromagnetic and nonferromagnetic bullets using CT. MATERIALS AND METHODS. Eight ferromagnetic, steel-jacketed lead bullets, four nonferromagnetic, non-steel-jacketed lead bullets, and four nonferromagnetic solid bullets composed of copper or copper and zinc alloys which we refer to here as "Cu(Zn) bullets," were scanned by CT at 80, 100, 120, and 140 kVp. Attenuation values (in Hounsfield units) were measured on an extended CT scale (ECTS) in the core and at the edge of the bullets and were used to calculate the dual-energy index (DEI). RESULTS. Although all nonferromagnetic bullets significantly differed from ferromagnetic bullets, the significant differences were solely attributed to the higher DEI of solid Cu(Zn) bullets compared with that of all-lead bullets. The lead bullets with ferromagnetic, steel-containing jackets did not differ from the lead bullets with nonferromagnetic, non-steel-containing jackets on the basis of DEIs obtained from core and edge measurements. Solid Cu(Zn) bullets could be clearly distinguished from lead bullets regardless of the metallic components of the jackets using DEI calculations from CT numbers on an ECTS. The DEIs based on the dual-energy pair 120 and 140 kVp appear to be the most appropriate for distinguishing between these two types of bullets. CONCLUSION. This study provides new scientific knowledge regarding metals and their characteristics at different tube voltage levels. The abilities of clinically approved dual-energy CT allow differentiation of bullets composed of low-atomic-number (Z) metals from bullets composed of high-Z metals via DEI calculations from CT numbers on an ECTS.

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Shooting samples were produced on standard textile pats of six different ammunition types: four ammunitions with exclusively infrared luminescent propellant powder particles, one containing a mixture of luminescent and non-luminescent particles and one with only non-luminescent particles. Unburned propellant powder particles in the gunshot residue (GSR) on the textile of each sample were transferred onto TLC-plates with the aid of an organic solvent. The patterns of the partially and the all-luminescent propellant powder residue on the TLC-plates were visualized in the near infrared wavelength range by the aid of an IR-sensitive camera. The transfer TLC-plates of all six ammunition types were sprayed with a diphenylamine solution, which reacts with the nitrate groups of the nitrocellulose and nitroglycerine and produces deep blue dots thereof. A series of samples with different shooting distances produced with one of the ammunition types was used for the shooting distance determination study. Transfer on TLC-plates was performed and pictures of the plates were taken before and after the chemical reaction. An imaging software was used to measure the density of the particles on the transfer TLC-plate pictures within a defined area around the bullet hole. Curves were drawn with the particle density data vs. the shooting distance. It has been shown, that the transfer of the particles onto a TLC-plate and the chemical reaction eliminate the limitations of the IR-method presented in Part I. Therefore, this method allows shooting distance determination at any textile and for any ammunition type as soon as unburned propellant powder particles are left on the target tissue.