## 4 Discussion
The number of GSR particles at the longest interval was between 542 in a nasal mucus sample [24] and less than 5 particles in a hand sample [25]. In this study, one or two GSR particles were identified on the shooter's hand after 4 and 5 h (the longest time interval) after firing low-caliber and high-caliber firearms, respectively. The time between the shooting incident and the GSR sampling is of particular importance, as it could greatly affect conclusions based on whether or not GSR particles are detected in a suspect's sample. Results based on single-shot tests revealed that GSR particles could be detected on the hand of a shooter who followed normal office activities for up to 4 h after firing, regardless of the season and type of firearm. The results showed that the main loss of GSR particles from a shooter's hands following routine office activity without hand washing occurred during the first 3 h after shooting in outdoor conditions (Figures 2 and 3). These observations are in agreement with the results presented by [PERSON] et al., which showed that the main loss of GSR occurred in the first 2-4 h after the shot; however, it should be noted that their tests were performed in indoor conditions [15]. Depending on the firearm used, GSR could be still identified 6 h after firing the weapon (Table 5). A decay in the particle loss was observed between 3 and 6 h, depending on the calibers and types of firearms used in this experiment. Five hours after the shooting, characteristic GSR particles were found in one of six series of experiments. Therefore, five hours could be proposed as a threshold for the time gap hypothesis, if it is assumed that only one shot was fired in the shooting event. As previously mentioned, one GSR particle has questionable significance [22], although in Kosovo it is still accepted as evidence. To overcome, at least partially, the uncertainty of the forensic conclusions, we can recommend the approach proposed by [PERSON] [18] but with a longer time interval. When more than five hours have passed since the shooting, GSR samples should also be collected from the suspect's face, hair, and clothing as well as his hands. In order to extract more information from SEM/EDS measurements, we calculated the mean number of characteristic GSR particles as a function of the postdischarge time (Figure 5). The obtained polynomial functions, presented in the Figure 5 inset, could be used to formulate an alternative hypothesis if it was assumed that only a single shot was produced during the shooting incident. The 6 % uncertainty of the SEM/EDS measurements should be taken into account. Therefore, if 25 \(\pm\) 2 GSR particles were found on the hand of a suspect, it can be assumed that a large-caliber ammunition was used and that the time interval between the shooting and sampling was approximately 2.5 h. If 10 \(\pm\) 1 GSR particles were identified, then two hypotheses could be made: (1) if high-caliber ammunition was used, the time interval was greater than 4 h, and (2) low caliber ammunition was used in this shooting event. However, it was observed that the individual results were highly scattered around the mean value due to the different weather conditions, the particularities of shooter's skin, the sampling irregularities, the type of firearm used, the person's activity, and the secondary transfer processes. Therefore, the proposed interpretation of the analytical results could only be used as a support tool for forensic specialists. According to [PERSON] et al., the evaluation of GSR analytical results obtained by SEM/EDS should be carried out in the context of specific circumstances of investigation, taking into account GSR transfer and persistence [26].