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

NCJ Number
Date Published
April 2019
13 pages
This is the Final Summary Overview report on a research project with the goals of explaining the physics of blood spatters from gunshots, improving the determination of the area of origin of these spatters with statistics and fluid dynamics, describing the interactions of stains with carpets, and providing the forensics community with high-quality and publicly available spatter patterns for teaching and research.

Using potential flow theory and the boundary conditions imposed by the bullet motion, the velocities impacted to the blood by the bullet impact were determined. The breakup of the blood upon impact was then described in the framework of the Rayleigh-Taylor instability, which occurs when a dense fluid (blood) breaks into drops when accelerated into a lighter fluid (air). Results of the model indicate that the size of the drops produced depends on their distance from the bullet path and on the bullet velocity and shape. Smaller, faster blood drops originate close to the impacting blunt bullet, and the larger and slower ones are formed further from it. Calculation of the drop trajectories is explained in this report. The discussion of the implications of this work for criminal justice notes that although this work is the first physical description of the production of a back spatter pattern due to gunshot, the implications are not immediate for criminal investigations. This is because the described project was a forward study in which results were obtained from known initial conditions; however, this does not create a model for reconstruction, in which initial conditions are determined from an inspection of the final conditions, i.e., the observed spatter. Two recommendations for crime-scene documentation are offered. Plans are underway for testing a reconstruction method with more spatters. 5 figures, 1 table, and 25 references

Date Published: April 1, 2019