Introduction
Forensic ballistics can be defined as the study of the projectile’s behavior to reconstruct the defining events in the production of a gunshot wound (GSW) and is divided into internal, external, and terminal ballistics [
1,
2]. While internal ballistics mostly focuses on the mechanisms of bullet ejection from the inside of the firearm, external ballistics describes the flight from the muzzle to the final target, and terminal ballistics, also referred to as wound ballistics, analyzes the injuries that occur in the different anatomical compartments.
The course of the bullet outside the barrel greatly influences the appearance of the GSW, especially when interaction with interposed objects, i.e., intermediate targets, occurs, which can cause alteration of the angle of incidence, tumbling and yawing of the bullet, resulting in an unstable flight and, ultimately, in atypical entrance wounds [
2,
3].
Intermediate targets are environmental objects opposing resistance to the projectile, causing deviation from the original trajectory, decrease in velocity, and so, dispersion of kinetic energy, which can lead to:
The GSWs produced by the modifications in the bullet’s behavior greatly differ from those occurring when the initial trajectory and stability remain unaltered [
3,
6,
8,
9]. An infrequently observed morphology of the entrance wound has been described in the literature as D-shaped when the surface of impact with the cutaneous tissue is represented by the lateral projection of the bullet [
2,
7,
8,
10,
11].
This peculiar appearance is given by an object with an acute angle at the apex and a recognizable cylindric base with regular margins. In fact, the forensic pathologist examining the wounds needs to interpret this finding and reconstruct the dynamics and the manner of death based on the collection of anatomical and circumstantial evidence. For the sake of the analysis conducted in this small but paradigmatic case series, the Authors relied on the similarities observed during the study of the intrasomatic bullet paths.
Two extremely different dynamics of production of D-shaped GSWs, where interaction with multiple (Case 1) and human (Case 2) intermediate targets was documented, are hereby presented, and analyzed. These examples are exceptional as in both cases the D-shaped conformation was demonstrated throughout the intrasomatic bullet path, from the entrance wound to the affected tissues.
Discussion
The interaction between the bullet and an intermediate target can result in peculiar GSWs which reflect the projectile’s behavior in space. In the two cases presented in this article, the entrance wounds’ morphology was characterized by a D-shape appearance, which was first described in 1984 by Donoghue et al. [
8] and is produced by the impact of the lateral surface of the bullet with the cutaneous surface [
2].
In case 1, the projectile’s course was first altered by the metallic wire fence, producing the well-known phenomenon of ricochet which occurs when the angle of incidence between the two objects is small, resulting in a tangential deviation from the original course [
7]. In this case, the contact with this intermediate target led to the dispersion of kinetic energy which was later accentuated by the impact with the rear window and the necklace worn by the victim. Specifically, the metal chain also produced an asymmetric abrasion collar and contusion ring, which was more prominent along the minor axis of the entrance wound. Moreover, the anatomical district itself, i.e., the cutaneous fold of the neck, contributed to the final appearance of both the entrance hole and the surrounding skin. For the exact same reasons, the exit wound showed similar findings when compared to the entrance, as while exiting the skin the bullet encountered the other portion of the necklace, producing a shored exit wound [
12].
In case 2, the D-shaped conformation was observed in the final target, i.e., the father, where the destabilizing factor was another human being that was trespassed and acted as an intermediate target: the bullet perforated the infant’s head and lost most of its kinetic energy, but still retained the capacity to cause damage and penetrate in the man’s chest. In this case, an additional element of interest is the comparison between the two entrance wounds which are both atypical but are the result of two different physical processes: the lesion on the infant’s head was produced by a stable bullet and had a long V-shaped projection because of the properties of the skull and the overlying scalp, while the lesion on the man’s chest is represented by a wobbling, destabilized bullet that had changed its orientation in space [
3].
In forensic literature, the D-shaped morphology has been described at the level of the cutaneous surfaces, while in the present case reports some structures throughout the intrasomatic bullet path were also characterized by the same finding. The study of the internal wounds warrants a few considerations for what concerns the physical characteristics of the anatomical districts.
In both the incidents presented in this article, the destabilized bullet produced the same results in terms of wounding effects, where the distribution and the morphology of the GSWs varied according to the different anatomical compartments.
First, structures like muscles and arterial wall in case 1, bone and liver in case 2, showed irregularly shaped wounds, leaving no traces that could reveal information about the bullet’s behavior. These tissues have limited stretch capacity in the case of GSWs and they were lacerated with fragmented margins, leading to a non-specific appearance of the wound.
On the other hand, the venous wall and the trachea in case 1, the pericardial sac in case 2, led to the production of the D-shaped morphology and allowed the examiner to clearly reconstruct the path, the orientation, and the rotation along its axis of the bullet throughout its course. These structures are more compliant to the energy and the displacement exerted by the bullet, especially when the velocity and therefore the temporary cavity effect are low. The GSWs at the level of the right ventricle were somewhat similar, where the D-shaped morphology could still be recognized despite the tissue recoil and the greater thickness when compared to the pericardium, which led to a less definite appearance of the bullet’s lateral surface.
The different behavior of the different anatomical districts varied according to the intrinsic mechanical properties of the structures and the thickness of the tissues drawn by the bullet. The jugular vein, the trachea, and the pericardium have thin elastic walls, which make them more compliant to the energy and the displacement exerted by the bullet, especially when the velocity and therefore the temporary cavity effect are reduced or neglegible. Instead, other vascular structures, like the carotid artery are thick, semi-rigid tubes.
Notably, the D-shaped morphology was seen exceptionally well at the level of the pericardium, perfectly reproducing the bullet’s impression on the thin fibrous tissue composing this membrane.
The discovery of the D-shaped morphology both upon external inspection and autoptic examination confirmed and supported the dynamics of wound production, which had been studied extensively by the crime scene investigation and FEG/EDS-SEM analyses and allowed the forensic pathologist to postulate that in both cases interaction with intermediate targets had occurred producing significant bullet destabilization with change in orientation and velocity.
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