New Research Reveals the Impact of Muzzle Gases on Bloodstain Patterns: Implications for Forensic Science

This new research reveals the importance of multiphase flow fluid mechanics in back spatter analysis, shedding new light on how forensic scientists can use this knowledge to reconstruct crime scenes and solve crimes.

Researchers from the University of Illinois Chicago and Iowa State University have made significant strides in improving bloodstain pattern analysis with the use of fluid dynamics. Blood back spatter, often found on crime scene surfaces or the clothing of accused criminals, is critical evidence in forensic investigations.

However, the complicated fluid dynamics of blood droplets and the interaction with muzzle gases from firearms can lead to misleading results if not correctly analyzed.

Through studying secondary atomization, the team was able to model the behavior of blood drops and gain insight into how this phenomenon impacts crime scenes.

Their findings, published in Physics of Fluids, shed light on the usefulness of multiphase flow fluid mechanics in back spatter analysis and the need to consider secondary atomization in future crime scene investigations.

“Primary atomization of blood is caused by a gunshot (bullet). It results in multiple drops spattered in the air,” explains author Alexander Yarin. “Some of these drops are big enough to be significantly distorted and torn apart by the air drag forces acting on a drop in flight. Smaller droplets arise during this process, which is called secondary atomization.”

After conducting experiments using various starting droplet sizes, the team verified their model and discovered a significant and predictable impact of secondary atomization. Specifically, their findings indicate that smaller droplets are more susceptible to being redirected towards the victim by the firearm’s gases during the crime, emphasizing the importance of considering this factor in back spatter analysis.

“Muzzle gases form a turbulent vortex ring which moves toward a victim from a shooter and pushes the blood droplets from the shooter back to the victim,” adds Yarin. “Droplets are also deflected aside, and our predictions showed that some can even land behind the victim, even though initially they were moving from the victim toward the shooter.”

This finding may shed light on how a shooter at close range could avoid getting blood stains on their clothing, as seen in high-profile cases such as the suspected murder of Lina Clarkson by Phil Spector, where Spector’s outfit remained remarkably clean.

“The results reveal the usefulness of multiphase flow fluid mechanics for the forensic discipline of back spatter analysis,” remarks Yarin. “Hopefully, code based on the present results would be used in future crime scene investigations.”

The research team plans to investigate the spatter of brain tissue in short-range shooting events in future studies. They anticipate that this work could potentially aid in differentiating between suicides and staged homicides, further advancing the field of forensic science.

Source: 10.1063/5.0142146

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