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How bloodstain 'tails' can point to significant, additional forensic details

Date:
November 21, 2023
Source:
American Institute of Physics
Summary:
Scientists demonstrate how bloodstains can yield valuable details by examining the protrusions that deviate from the boundaries of otherwise elliptical bloodstains. The researchers studied how these 'tails' are formed using a series of high-speed experiments with human blood droplets less than a millimeter wide impacting horizontal surfaces at various angles. They found that the tail length can reflect information about the size, impact speed, and impact angle of the blood drop that formed the stain.
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Forensic science has captured the public imagination by storm, as the profusion of "true crime" media in the last decade or so suggests. By now, most of us know that evidence left at a crime scene, such as blood, can often reveal information that is key to investigating and understanding the circumstances around a crime -- and that scientific methods can help interpret that information.

In Physics of Fluids, by AIP Publishing, a group of scientists from Boston University and the University of Utah demonstrated how bloodstains can yield even more valuable details than what is typically gathered by detectives, forensic scientists, and crime scene investigators. By examining the protrusions that deviate from the boundaries of otherwise elliptical bloodstains, the researchers studied how these "tails" are formed.

"These protrusions are typically only used to get a sense of the direction that the drop traveled, but are otherwise neglected," said author James Bird.

In fact, previous studies have primarily focused on larger blood drops falling vertically on flat surfaces or on inclined surfaces where gravity can reshape and obscure the tails. By contrast, the new study involved a series of high-speed experiments with human blood droplets with diameters of less than a millimeter impacting horizontal surfaces at various angles.

"We show that the precise flow that determines the tail length differs from the flow responsible for the size and shape of the elliptical portion of the stain," said Bird. "In other words, the tail lengths encompass additional independent information that can help analysts reconstruct where the blood drop actually came from."

Indeed, the tail length can reflect information about the size, impact speed, and impact angle of the blood drop that formed the stain. When measured for several blood stains in a stain pattern, the trajectories of the drops can be backtracked to their presumed origin.

While their analysis employed only horizontal surfaces to examine impact velocity dynamics, Bird and his colleagues hope it triggers more studies that focus on the length of the tail in bloodstain patterns. They believe that incorporating tail length into standard bloodstain analyses will produce more robust evidentiary information.

"Knowing the origin of the blood stains at a crime scene can help detectives determine whether a victim was standing or sitting, or help corroborate or question a witness's testimony," said Bird.


Story Source:

Materials provided by American Institute of Physics. Note: Content may be edited for style and length.


Journal Reference:

  1. Garam Lee, Daniel Attinger, Kenneth F. Martin, Samira Shiri, James C. Bird. Bloodstain tails: Asymmetry aids reconstruction of oblique impact. Physics of Fluids, 2023; 35 (11) DOI: 10.1063/5.0170124

Cite This Page:

American Institute of Physics. "How bloodstain 'tails' can point to significant, additional forensic details." ScienceDaily. ScienceDaily, 21 November 2023. <www.sciencedaily.com/releases/2023/11/231121175242.htm>.
American Institute of Physics. (2023, November 21). How bloodstain 'tails' can point to significant, additional forensic details. ScienceDaily. Retrieved February 23, 2024 from www.sciencedaily.com/releases/2023/11/231121175242.htm
American Institute of Physics. "How bloodstain 'tails' can point to significant, additional forensic details." ScienceDaily. www.sciencedaily.com/releases/2023/11/231121175242.htm (accessed February 23, 2024).

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