New research in forensic science has revealed that the “tail” of a bloodstain provides important information about the origin of the blood droplet, enhancing crime scene analysis and evidence interpretation.
Forensic science has taken the public imagination by storm, as evidenced by the abundance of “true crime” media over the past decade or so. Evidence such as blood left at a crime scene can now reveal key information for investigating and understanding the circumstances of a crime, and scientific methods can help interpret that information. , now almost everyone knows.
in fluid physicsA group of scientists from Boston University and the University of Utah have demonstrated in AIP Publishing how bloodstains can yield even more valuable details than those typically collected by detectives, forensic scientists, and crime scene investigators. The researchers studied how these “tails” form by examining protrusions that deviate from the boundaries of oval bloodstains.
“These protrusions are typically only used to figure out the direction in which the droplet has moved, and are otherwise ignored,” says author James Byrd.
In fact, previous studies have mainly focused on large blood droplets that fall vertically onto flat or inclined surfaces, where gravity can distort the shape of the tail and make it difficult to see. In contrast, the new study involved a series of high-speed experiments in which droplets of human blood, less than a millimeter in diameter, were bombarded with horizontal surfaces at different angles.
“We showed that the precise flow that determines the length of the tail is different from the flow that is responsible for the size and shape of the oval part of the stain,” Bird said. “In other words, the tail length contains additional, independent information that helps analysts reconstruct where the blood drop actually came from.”
Indeed, the tail length may reflect information about the size, impact velocity, and impact angle of the blood droplet that formed the stain. Measuring multiple blood stains within a stain pattern allows the trajectory of the droplet to be traced back to its presumed origin.
Although their analysis only used horizontal planes to examine impact velocity dynamics, Byrd and colleagues hope this will spark further research focusing on the tail length of bloodstain patterns. Masu. They believe that incorporating tail length into standard bloodstain analysis will provide more robust evidence information.
“Knowing the origin of bloodstains at a crime scene can help detectives determine whether the victim was standing or sitting, and corroborate or challenge eyewitness testimony,” Byrd said. said.
Reference: “Bloodstain Tail: Asymmetry helps reconstruct oblique shocks” by Garam Lee, Daniel Attinger, Kenneth F. Martin, Samira Shiri, and James C. Byrd, November 2023 21st of the month fluid physics.