The dynamics of sharp force trauma and subsequent bloodspatter

Abstract

The examination of a crime scene is a highly complex process. Owing to this notion, crime scenes are often reconstructed, in order to gain greater insight as to the sequence of events that took place during the commission of the crime. Due to the high complexity involved in both crime scene reconstruction and also bloodstain pattern analysis, it is near impossible to recreate a wounding event precisely. Therefore, it is imperative to strive for as much accuracy and realism as possible when conducting recreation experiments. Sharp force trauma is a common means of assault or homicide in countries where access to firearms is restricted, for example New Zealand. Due to the high prevalence of sharp force trauma attacks in this country, it is necessary to gain as much insight into the dynamics of sharp force events, so as to provide information that may potentially aid in a related crime scene. In order to investigate sharp force trauma impacts, a receiving target is needed that simulates the human body with as much accuracy as possible. The present study aimed to develop and validate a non-biological soft tissue simulant that can be used for simulating sharp force events and subsequent bloodspatter recreation. The non-biological model consisted of three distinct tissue layers, attached together to form one complete unit. The uppermost layer used silicone to simulate human skin; the inferior layer was made from polyurethane foam, with the purpose of simulating subcutaneous tissue and the foundation of the model consisted of gelatin, functioning as muscle tissue. Gelatin was decided upon due to its extensive use as a muscle simulant in ballistic testing. The use of gelatin in this study subsequently required validation and this was achieved by reviewing the literature and comparing the similarity in maximum velocity, following penetration, between the model and pork tissue. In order to understand the dynamics and production of bloodspatter from sharp force trauma events, laboratory simulated sharp force trauma events were conducted and captured using a high-speed digital video; allowing for fast occurring actions to be analysed in slow motion. Recordings from each simulated sharp force event could be played back in slow motion, enabling the kinematics of a stabbing and resultant bloodspatter to be easily observed. Two main mechanisms of bloodspatter were determined from the high-speed videos, corresponding to impact spatter and cast-off. This provides valuable forensic information that can be applied to criminal situations involving bloodspatter from a sharp force trauma event.