Finding the Region of Origin of Bloodspatters in Complex Situations: Novel Physics-Based Methods and Tools

As submitted by the proposer: We propose a collaborative research project between two experts in fluid dynamics (with clearly defined roles), one textile expert and one bloodstain pattern analyst. The research outcome will deliver novel physics-based methods and tools for finding the region of origin of a blood spatter in two complex situations: (a) spatters generated from a jet or stream of blood (arterial gushing, expectorate, gunshot), and (b) spatters on the complex absorbing surfaces of carpets. In both cases we will combine innovative experiments and theory to answer the following question: What is the region of origin of the blood spatter? While the disciplines of bloodstain pattern analysis (BPA) in forensics and that of fluid dynamics (FD) each have a rich history, interactions between these communities have not always been strong. The need for better integrating FD and BPA is mentioned in a 2009 report [1] by the US National Research Council, entitled "Strengthening Forensic Science in the United States: A Path Forward". The report advocates for stronger scientific foundations for BPA, given "the complex nature of fluid dynamics". From our recent work, we are convinced that the FD and BPA communities could benefit from a deeper understanding of each other. Specifically, by following the path proposed by the US National Academies, BPA can obtain new quantitative tools and methods, while FD may be presented with new flow problems. Blood spatters are deterministic signs of a violent crime. Bloodstain Pattern Analysis is however not straightforward, because the physical relation between blood impact and the resulting bloodstains is non-linear. Indeed, the formation of blood spatters involves a complex fluid (the blood), a complex atomization process involving fluid mechanics, heat and mass transfer, the flight of drops through air including their deformation and possible secondary breakup, and the impact of drops on surfaces with varying roughness and wettability. The PI has recently developed a method to reconstruct the backward trajectories of impact spatters, based on 3D inspection of stains. The proposed research will investigate more complex situations: In the first case, we will consider spatter mechanism that are jet-like, where aerodynamic effects and interactions between drops modify the drag and might drastically increase the range of trajectories, in a comparable manner to formation flight of birds that allow them to travel further away than by their sole force. We will develop a theory validated by experiments, and provide BPA analysts with charts to account for this complex effect, which has been key to e.g. Stuart James testimony in the Phil Spector case. A second problem is related to the inspection of drip stains on carpets. We recently unlocked several complex phenomena of the related fluid dynamics, including a new inertial focusing mechanism. We will transition these new findings to the field of BPA, and provide tools to the BPA investigator to determine the height from which the dripping stains have been generated. We will use existing and high-level contacts within the BPA and fluid dynamics community to disseminate our results, and organize a workshop to transition the findings and methods to the community. ca/ncf