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Appearance and characteristics of the gunshot wounds caused by different fire weapons – animal model

Gesundheitszentrum Odenwaldkreis, Internal medicine, Erbach, Germany; University of Belgrade, Faculty of Medicine, Institute of Medical Statistics and Informatics, Serbia; University of Sarajevo, Faculty of Medicine, Department of forensic medicine, Bosnia and Herzegovina; University of Priština (temporary residence in Kosovska Mitrovica), Faculty of Medicine, Institute for forensic medicine, Kosovo, Serbia


INTRODUCTION
Throughout history, ballistics experts and forensic medicine experts have classified gunshot wounds with respect to range by a variety of methods. All of these methods include inspection and comparison with test firings or patterns of gunshot residues (GSR) at a wound site [1].
Firearm-related injuries are a leading cause of morbidity and mortality in the world. In many shooting cases, bullets hit surfaces of various parts of the human body (often the head) directly.
For the purpose of assessing the shooting distance, most of the forensic literature describes only visual/microscopic methods for examination of the wound appearance and discharge 3 particle patterns around. Shooting distances from human body surfaces can be divided roughly into four ranges: contact, near contact range, intermediate range and distant range [2,3]. In contact wounds, the muzzle of the weapon is held against the surface of the body at the time of shooting. The appearance of tearing, scorching, soot, or the imprint of the muzzle characterizes contact wounds. In near contact wounds, the muzzle of the weapon is not in contact with the skin, being held a short distance away (a few centimeters). Characteristic of this kind of gunshot is a wide zone of powder soot overlaying seared blackened skin around the entrance wound.
Intermediate range gunshot wound is one in which the muzzle of the weapon is held away from the body at the time of discharge, but is still close so that gunpowder expelled from the muzzle can produce "powder tattooing" of the skin [4].
An impact velocity of only 150 to 170 fps is required to penetrate skin. Most entrance wounds, regardless of range, are oval to circular with a punched-out clean appearance and are often surrounded by a zone of reddish damaged skin (the abrasion ring).While powder tattooing of the skin implies a close-range wound, the fact that there are different forms of propellant powder makes this an unreliable finding. Also, indicative of a close-range injury is a cherry hue appearance of underlying muscle due to carboxyhemoglobin, formed by carbon monoxide release during combustion [5].
Wound diameters and only visual analysis of dispersion of gunshot residues (GSR) are used in practice, like some kind of screening method, just to check does it fit to the known story from crime scene, etc. fire range. Previous studies have pinpoint that the caliber of the bullet that caused an entrance wound in the skin cannot be determined by the diameter of the entrance. A .38-caliber (9-mm) bullet can produce a hole having the diameter of a .32 caliber (7.65-mm) bullet and vice versa. The size of the hole is due not only to the diameter of the bullet but also to the elasticity of the skin and the location of the wound. An entrance wound in an area where the skin is tightly stretched will have a diameter different from that of a wound in an area where the skin is lax. Bullet wounds in areas where the skin lies in folds or creases may be slit-shaped [2].
The size of an entrance hole in bone cannot be used to determine the specific caliber of the bullet that perforated the bone though it can be used to eliminate bullet calibers. Thus, a bullet hole 7.65 mm in diameter would preclude it having been caused by a 9-mm (.38 caliber) weapon. Bone does have some elasticity, however, so that a 9-mm bullet may produce a 8.5mm defect.
In earlier ages, researchers tried to prove potential usage of wound size, its surface area, but results were very inconclusive. Gunshot residues on the skin of a victim are important evidence, with far better precision, for reconstructive questions in the forensic investigation of cases involving gunshot wounds [3]. Powder soot may help to differentiate between entrance and exit wounds, draw conclusions on the muzzle-to-target distance and on the muzzle-target angle [5,6]. Gunshot residue (GSR) consists of particles composed of antimony, barium and lead that arise from the condensation of primer vapors [3] and also soot debris consisting of carbon and metallic fragments [6] In recent times there weren't any studies that tried to determinate or to exclude type of weapon or distance between body and weapon with only wound characteristics.
The aim of this experimental study is to analyze is there any significant difference in macroscopic characteristics of wounds that were caused with different types of weapons from three different distances.

MATERIALS AND METHODS:
Study is conducted in Department of Ballistic and Mechanoscopic Expertise, Center for Forensic and Information Support, Federal Police Directorate. Study is performed in accordance with the ethical principles in compliance with the law on the protection of animals in our country. Study is approved by Ethical committee of Medical Faculty at University of Sarajevo and used data is part of the author PhD thesis (Figures 1 and 2).
Sample subject is pig ( Figure 1). In total 30 shooting pigskin was used, on which 60 shooting were made, but 5 of them due to the technical errors weren't included in analyzes. Part of the pig body size is approximately 120 x 45 x 20 m composed of skin, subcutaneous and muscle tissue, areas of the chest and abdomen, which is attached to a solid surface. Shooting was conducted using a system for safe firing from the firearm (Verifire-The Secure Firing Device, Twin Tooling, Canada) ( Figure 3). Samples of the pig skin was shot by firing projectiles from four different weapons and from three different distances (contact wound, and near contact wound, 5 cm and 10 cm) ( Figure 4). The weapons used in the experiment were most commonly used in the Balkan region in last 10 years according to Federal and local police. Characteristics of weapons and projectiles are presented in (Table 1, Figure 3). Because it was done in experimental conditions and using firearm device all samples were included in analyses ( Figure   3, Table 1).
After shooting the dimensions of the wound, contusion ring, and the area of scattering of gunshot powder particles were measured. Based on these dimensions we have made calculation of the wound area. As a model of surface rhombus was taken into account ( Figure 4).

Statistical analysis
Results are presented as count (percent) or median (interquartile range) depending on data type.
Fisher's exact test was used to assess significant differences between groups regarding nominal variables. Mann-Whitney U test was used to test the differences between different weapons regarding interval data. No adjustment method for p values were used due to small sample size and experimental nature of the study. All data were analyzed using SPSS 20.0 (IBM Corp.

RESULTS:
In total 55 wounds were analyzed, caused with four different weapons and from three different distances. Distribution based on the range was very similar, with no statistically significant difference in distribution, Fisher's Exact test p = 0.992 (Table 2).
First, we have tested is there any significant difference in any of examined characteristics of wound in total, without considering range of firing. No significant difference was found in the horizontal diameter of the wound, vertical diameter of the wound, or even surface between four different calibers. Contusion ring in the narrowest and in the widest diameter has significantly different values; furthermore, area of GSR was significantly different between tested calibers (Table 2.). We did comparison of wound characteristics caused with pistols, and based on that we have concluded that widest and narrowest parts of contusion ring significantly differ (widest p = 0.002, narrowest p = 0.005), as do GSR scattering area p = 0.036. At the contact range; wounds caused with automatic rifle had horizontal, vertical diameters significantly larger than those made by pistols (p < 0.05 vs. tested pistols). Diameters on the gunshot wounds that were caused with different pistols, were very similar and none of them was statistically different (p > 0.05) (Table 3).  between horizontal diameters when firing was with direct contact on skin and from 5 cm range (p = 0.04), also comparing wounds from direct contact between pistol and skin and those from 10 cm range, there was significant difference (p = 0.007). Horizontal diameters of wound didn't statistically differ when comparing those from 5 cm and 10 cm range.
Pistol with 9 mm caliber caused much smaller wounds when firing from 5 od 10 cm than those that were caused from direct contact (vs. 5 cm p = 0.001; vs. 10 cm p = 0.001). Also vertical diameter was significantly smaller on wounds caused from 10 cm range than from direct contact (p = 0.004). Surface area of the wound is decreasing with the increase of the distance (p = 0.001).
Widest part and narrowest part of CR differ when using pistol with 7.65 mm caliber, measuring from three different fire ranges (p = 0.005). Also GSR surface area had significantly different values (p = 0.002), with trend of GSR area increasing with increase in distance. GSR surface area had significant change in value due to the change of fire range (p = 0.049). This was due to the smaller size of GSR scattering area when firing at the direct contact.
Statistically different values of widest (p = 0.007) and narrowest part of CR (p < 0.001) were measured on wounds caused with 9 mm pistol from different distances. Also GSR scattering area significantly differ based on distance (p = 0.002). Automatic rifle had statistically different values of widest and narrowest part of CR, based on distance (p = 0.002 and p = 0.057 retrospectively). There was no difference between wounds that were caused from 5 and 10 cm (p > 0.05). GSR surface area also significantly differ between different distances, as surface widens with increase of distance (p = 0.027).

DISCUSSION:
Small number of papers is done on this topic. In practice we are searching for efficient, practical and cheap methods that could be used for determination of firing distance and caliber. wounds were significantly different (p < 0.001) [7].
In our experiment no matter which weapon we have used, there wasn't any significant difference between 5 and 10 cm range. Both of these values are categorized in near contact range, but diameters are decreasing with increase of distance. There aren't any papers that have tested ranges that were so close.
Karen Isha Sahu et all. have in their study on cotton cloth sheet, wound caused with 9 mm pistol had similar gunshot patterns as our results. Horizontal diameter was wider for all the patterns at 5 cm range, but at 10 cm blackening was more dominant [8].
In our study, we used geometrical shape of rhomb. Matoso et all. [9] in their study have proven that different morphologies in the entrance holes are produces by three different calibers, using the same skull at the same shot distance of 10 cm. 9 mm wound was irregular, triangular, while 10 mm caliber was round.
At the contact, in the comparison of wounds caused with different weapons, the values of widest and narrowest part of contusion ring around the wound in total are significantly different (p=0,003 and p=0,004 retrospectively). Independently we found that contusion ring at close range (contact) had similar widest part diameter when firing from pistol with 7,62 mm, pistol with 9 mm or with automatic rifle with 7,62 mm caliber (p>0,05).
Gunpowder residues scattering area significantly differ between weapons when firing from close contact (p=0,007). Turillazi et all. (10] in their study showed that at 0.2 cm distance circumferential blackening with soot deposited in zone around entrance was, while on 5 cm, a wide zone of powder soot overlying seared blackened skin was evident in the wound. Also area median when 7.65 mm and 9 mm caliber were used wasn't significantly different. These results are in regard with our results. Authors have proven that GSRs deposits in the skin surrounding entrance wounds strictly correlate with shooting distance. In our study GSR surface area had significantly different values (p=0,002) when comparing calibers, with trend of GSR area increasing with increase in distance. This is explained with a fact that both ranges 5 cm and 10 cm are categorized in near contact range. Intermediate range has a smaller GSR area, and in contact wounds with 0° angle, GSR are in the wound channel [10].

9
Also, narrowest parts of contusion ring could be used for determination between calibers, even between pistols. There is almost no difference between 7.65 mm caliber and 9 mm caliber.
Creating a computer software for calculation of wound area is one of the goals in future. Petruk Vasyl et all. discussed multispectral method and means for determining the distance of the shot on the skin tissues. Using the computer model they made an output of the expert system to generate diagnostic solution in the form of the distance to the target. They made a neural network. Multispectral improved method and means for determining the distance of shooting on the basis of the study gunshot injuries of the skin tissues, which allows to register the skin damage biological tissue forensic expert and use the findings as an evidence base [11]. histologically identified in many skin, soft tissue, and bone sections at all ranges with tested calibers. These nonparallel results decrease the dependability of histology for range of fire estimation and reinforce using gross observation. [14].

Limitations of study:
Small number of samples and only three ranges were included in this study. In future studies intermediate range and long range gunshot wounds should be taken into account and analyzed.
In addition, we have made this experimental study on pig skin, more precise data would be collected from experiment which is done on cadaver skin.

CONCLUSION:
New study on larger sample should be conducted, that would include not only experimental conditions, but also in outside real conditions. Also, computer software that would automatically analyse wound dimensions should be made for easier work. Based on this small sample, vertical and horizontal diameters, also wound surface area are useful for differentiation between pistol and rifle caused wounds from contact and near close range. It is unsecure method for determination of pistol caliber or fire range.
Gunshot residues have much greater potential for future analyses, but even GSR can't be used to determinate pistol caliber. It can be used to determinate rifle inflected wounds, as it had significantly higher values then GSR scattering area around the pistol inflected wounds. In the case if there is known weapon, GSR scattering area can be used to determinate range. Since real-time shots were made at various angles, it is necessary to introduce a correction coefficient.

ACKNOWLEDGMENT:
We would like to express our utmost gratitude to the Department of Ballistic and    The size of the wound was determined using five points. One central point, was taken and around it the others. In one clockform, up to 12h, 3h, 6h and 9h. The values of surface area were calculated using the rhombus as a model.