Charon’s Coins

In situ identification of Action 4, SECA and QD-PEP bullets from special police ammunitions by computed tomography

INTRODUCTION

Special deformation bullets were developed for police forces to achieve a defined penetration depth (avoiding over-penetration) and a controlled energy transfer (avoiding collateral damage). This article focuses on Action 4, SECA and QD-PEP bullets. These 9 mm bullets were specially designed for controlled deformation. The characteristic slight mushrooming with a front cross-section of approximately 11.5 mm after entering a ballistic simulant was verified in ballistic tests. To achieve such slight mushrooming, the projectile's core is hollowed. The purpose of this study was to investigate the feasibility of visualising the hollowed cores of Action 4, SECA and QD-PEP bullets using a standard clinical computed tomography (CT) scanner for non-invasive identification of these special bullets from police ammunitions.

METHODS

First, undeformed specimens were scanned to reveal the shape of the hollowed core of each type of special bullet. Second, Action 4, SECA and QD-PEP bullets were fired towards animal cadaver models to visualise their hollow core after deformation inside biological tissue. Third, two reviewers were tasked with identifying special bullets from police ammunition (Action 4 bullets: n = 3) among 10 CT examinations of humans with lodged projectiles who were selected by the supervisor of the study.

RESULTS

The CT scans of the undeformed specimens revealed the special design of the bullets' metal core. All special bullets from police ammunitions that were fired towards an animal cadaver model demonstrated the characteristic slight mushrooming. In accordance with the CT scans of the undeformed bullets, visualisation of the individual internal cavities of the special bullets allowed the Action 4, SECA and QD-PEP bullets to be clearly distinguished. With regard to the real forensic cases, both reviewers clearly identified each of the three Action 4 bullets among all other lodged projectiles.

CONCLUSIONS

This study demonstrates the feasibility of identifying Action 4, SECA and QD-PEP bullets from special police ammunitions by CT. The individual shapes of the cavity inside the bullets were clearly visible on CT. In situ identification of these bullets can aid in the assessment of injuries, and since these bullets are fabricated from non-ferromagnetic metals, their clear identification allows for magnetic resonance imaging (MRI) without the risk of bullet movement inside the body due to the magnetic pull of the MRI unit. Furthermore, this approach could be of great interest to forensic investigators if patients who received gunshot wounds underwent non-operative treatments and the projectile remains in the body. Since the use of CT is also increasing for medico-legal post-mortem examinations, the identification of lodged projectiles is of interest for a virtual autopsy or 'Virtopsy'.

Pandora's box

Suitcases or other containers are occasionally involved in forensic investigations. If there is a suspicion that human remains are hidden inside such a container, medico-legal examinations are required. However, these containers are occasionally locked. Forced opening of a locked suitcase or container may cause damage to its contents. Additionally, the safety of the investigator has to be considered as such containers may be booby-trapped or contain other hazardous material. An overview of the contents before opening is desirable in order to avoid the possibility of encountering a Pandora's box. In forensic medicine, an established approach to examine the inside of a body before opening at autopsy is postmortem computed tomography (CT). However, there may be a reluctance to use this approach for suitcases or containers with metallic components because of the assumption that severe metal artifacts will result in inadequate images. In this article, we present a forensic case in which a CT scan of a metallic suitcase was performed in order to examine its contents. Additionally, we performed an experimental scan of a conventional safe in order to determine if CT is able to reveal the contents of such a highly radiopaque storage box.

Post-mortem computed tomography: Technical principles and recommended parameter settings for high-resolution imaging

Post-mortem computed tomography (PMCT) has become a standard procedure in many forensic institutes worldwide. However, the standard scan protocols offered by vendors are optimised for clinical radiology and its main considerations regarding computed tomography (CT), namely, radiation exposure and motion artefacts. Thus, these protocols aim at low-dose imaging and fast imaging techniques. However, these considerations are negligible in post-mortem imaging, which allows for significantly increased image quality. Therefore, the parameters have to be adjusted to achieve the best image quality. Several parameters affect the image quality differently and have to be weighed against each other to achieve the best image quality for different diagnostic interests. There are two main groups of parameters that are adjustable by the user: acquisition parameters and reconstruction parameters. Acquisition parameters have to be selected prior to scanning and affect the raw data composition. In contrast, reconstruction parameters affect the calculation of the slice stacks from the raw data. This article describes the CT principles from acquiring image data to post-processing and provides an overview of the significant parameters for increasing the image quality in PMCT. Based on the CT principles, the effects of these parameters on the contrast, noise, resolution and frequently occurring artefacts are described. This article provides a guide for the performance of PMCT in morgues, clinical facilities or private practices.