High-Speed Video Analysis of Forward and Backward Spattered Blood Droplets

High-speed videos of blood spatter due to a gunshot taken by the Ames Laboratory Midwest Forensics Resource Center (MFRC) were analyzed. The videos used in this analysis focused on a variety of targets hit by a bullet that caused either forward, backward, or both types of blood spatter. The analysis process used particle image velocimetry (PIV) and particle analysis software to measure drop velocities, as well as the distributions of the number of droplets and their respective side-view area. The results of this analysis revealed that the maximal velocity in the forward spatter can be about 47 +/- 5 m/s and for the backward spatter about 24 +/- 8 m/s. Moreover, measurements indicated that the number of droplets produced is larger in forward spatter than it is in backward spatter. In the forward and backward spatter, the droplet area in the side-view images was approximately the same. The upper angles of the close-to-cone domain in which droplets were issued in forward and backward spatter were, 27 +/- 9 degrees and 57 +/- 7 degrees , respectively; whereas, the lower angles of the close-to-cone domain were 28 +/- 12 degrees and 30 +/- 18 degrees , respectively. The inclination angle of the bullet as it penetrated the target was seen to play a large role in the directional preference of the spattered blood. Also, muzzle gases, bullet impact angle, as well as the aerodynamic wake of the bullet greatly influenced the flight of the droplets. (Publisher abstract modified)