Implications of Two Backward Blood Spatter Models Based on Fluid Dynamics for Bloodstain Pattern Analysis

• NCJ Number: 254208
• Author(s): P. M. Comiskey; A. L. Yarin; D. Attinger
• Date Published: August 2019
• Length: 7 pages
• Grant Number(s): 2014-DN-BX-K036; 2017-DN-BX-0171
• Agencies: NIJ-Sponsored
• Publication Type: Research (Applied/Empirical); Report (Study/Research); Report (Grant Sponsored); Program/Project Description
• Award: Finding the Region of Origin of Bloodspatters in Complex Situations: Novel Physics-Based Methods and Tools; Ultrafast 3D visualization and fluid dynamic mechanisms of blood atomization

Annotation

Since more sophisticated models for blood spatter trajectory reconstruction are being developed, this article highlights two that enable the prediction of bloodstain patterns produced from backward spattered blood droplets from blunt and sharp bullets.

Abstract

Bloodstain pattern analysis (BPA) is an integral part of crime scene investigation. For violent crimes involving gunshots, standard practice in police departments worldwide have some physical limitations. For instance, the effect of gravity and air drag on trajectories of blood droplets are neglected in current reconstruction methods, which results in a well-known overestimation of the height of the source of blood. The recent models profiled in this article attribute the splashing of blood to the Rayleigh-Taylor instability which arises when blood is accelerated towards lighter air. This physically based description comes with the predictive capability to correlate features of bloodstain patterns with the specific bullet and gun that produced them, as well as with the body position. The results of the numerical models were compared with four experiments that simulated blood spatter deposition on a vertical wall through the number of stains produced, average stain area, and average impact angle at the surface. The agreement found is fairly good; moreover, further insight is obtained by probing and explaining the influence of observable parameters on the resulting spatter pattern, with the goal of aiding BPA experts evaluating a crime scene. (publisher abstract modified)