## 4 Discussion  
The identification of the GSR by SEM/EDS is a standard method used by justice authorities in the Republic of Kosovo. Currently, only the characteristic particles of the GSR determined by SEM/EDS are accepted as evidence of a person involved in or in the vicinity of a shooting incident. According to the ASTM classification, the particles characteristics of GSR are three-component spheroidal particles containing PbBaSb. A single PbBaSb-containing particle detected by SEM-EDS is considered evidence, regardless of the reported questionable significance of one or two GSR particles in a sample [22]. Thus, this study focused on the particles characteristic of GSR identified by SEM/EDS and produced by discharging weapons typically found in the criminal incidents in the Kosovo region. Although an indispensable tool in forensic investigation, GSR research by SEM/EDS is time-consuming and expensive. Thus, we attempted to extract more information from SEM/EDS data by considering the number of detected characteristic GSR particles. A detailed optimization and validation of the SEM/EDS protocol in the laboratory of the Kosovo Forensic Agency was presented in our previous paper [12]. Based on the method's performance, estimated for each group of characteristic GSR particles in the reference sample SPS-SP-2A (Table 4), i.e., repeatability, within-laboratory reproducibility, sensitivity, and bias, the method was assessed as \"fit for purpose\" according to the requirements of  
Figure 6: Number of particles characteristic of GSR as a function of time after discharge of a high-caliber Zastava M70 AB2 rifle (blue line) and a low-caliber Glock 19 pistol (9 \(\times\) 19 mm) (orange line). ASTM 1588 [9] for the intended use of results by courts, prosecutors, and police intelligence in the Republic of Kosovo. The forensic practice in the Republic of Kosovo revealed that firearms are often used by criminals, reflecting the state in the region after the 1998-1999 war. The data showed that the same firearms were used in many cases, but ammunitions came from different European manufactures. The UN report presented in 2003 revealed that 460,000 civilian small arms could be found in Kosovo region, and 53% of the reported guns were Zastava and Tokarev, while 85% of the assault rifles were Kalashnikov and Zastava [23]. Three high-caliber (Zastava and RPD) and three low-caliber (Walter, Glock, and Zastava) firearms were included in this study (Tables 1 and 2). Based on data from the Kosovo Forensic Agency's ballistics laboratory, the studied weapons and ammunition were those most frequently used in criminal proceedings for which the Kosovo Prosecution and Court required expertise. Additionally, weapons presented for legalization and registration in the Integrated Ballistics Identification System (IBIS) database were included in the tests. The low-caliber Glock 19 pistol used today by the Kosovo police was also studied. The results from the tests with low- and high-caliber firearms (Table 6 and Figure 4) showed that the low-caliber firearms generated, on average, 25% of the total number of detected GSR particles that originated from high-caliber ammunition discharge. The obtained result was logically related to the quantity of the ammunition components. The GSR persisted on a shooter's hand for approximately 4-5 h, depending of the caliber of the weapon fired if a single shot was made. However, GSR generated from firing a Zastava rifle was found after 6 h normal daily activity (Tables 5 and 6). The results are in agreement with the findings reported in the literature: characteristic GSRs were identified by SEM/EDS from 4 to 10 h after firearm discharge [3]. [PERSON] [18] estimated that the average half-life of the GSR on the hands of five shooters making nine shots reached up to 30 min, while it reached 170 min on the face and hair. The GSR detection time intervals by SEM/EDS reported in the literature varied from 4 h for hand samples to 48 h for nasal samples [3; 24].