Analysis of Bloodstains Aids Detectives in Developing Fresh Insights for Investigations
Forensic investigations often rely on the analysis of bloodstain patterns to piece together the events of a crime scene. A new study published in Forensic Science International, titled "Dynamics of blood falling on three types of cotton fabrics and resulting bloodstains," sheds light on how the velocity of blood spatter influences the formation of bloodstains on different types of cotton fabrics, and how this information can aid in crime reconstruction [1].
The research, led by Fujun Wang, a former Ph.D. student at NC State, and co-authored by Vanessa Gallardo, a former postdoctoral researcher at NC State, and Stephen Michielsen, a former professor in NC State's Wilson College of Textiles who is now on faculty at RMIT University in Australia, focuses on the distinct features that high-velocity blood spatter creates on plain woven, 3×1 twill, and jersey knit cotton fabric.
One of the key indicators of velocity is the presence of satellite droplets, tiny stains surrounding a central stain. These droplets increase in number with higher impact velocity. Bloodstains with many "fingers" or elongated extensions also suggest faster-moving blood at the point of impact, although these fingers may spread or merge over time [1].
The study found that the final stain sizes were nearly independent of the impact velocity, but strongly dependent on the fabric structure. Plain-woven cotton, for instance, provides more reliable and interpretable bloodstain patterns, making it easier for forensic experts to read velocity indicators such as satellite droplets and finger-like extensions. In contrast, twill-woven cotton tends to complicate pattern interpretation, making it more difficult to extract precise velocity-related information from the stains [1].
The physical properties of plain-woven cotton make it easier to estimate the velocity of blood spatter compared to other fabrics. High-speed cameras captured the impact of the blood on the fabric and the way it traveled through the fabrics over time. The researchers splashed these fabrics with porcine blood treated to ensure consistency, applied at 12 different velocities [1].
The researchers found that the 'fingers' of the blood stain, thin tendrils that spread out from the center of the stain, correlate with the velocity of the blood spatter. This correlation can provide additional information for forensic investigations.
The study also developed empirical power-law-based models to predict wicking kinematics, the splashing threshold, and the number of satellite droplets during splashing. Comparison with experimental data demonstrates the model's adequacy in describing wicking kinematics [1].
The researchers are interested in doing additional work with a wider variety of fabrics, weaves, and yarns to further improve forensic bloodstain pattern analysis. The National Institute of Justice under grant 2018-R2-CX-0033 supported this study [1].
Understanding how blood impacts different cotton weaves can significantly assist forensic investigators in reconstructing crime scenes by better estimating the velocity of blood spatter and movement, which is essential for accurate event reconstruction [1].
[1] Wang, F., Gallardo, V., & Michielsen, S. (2021). Dynamics of blood falling on three types of cotton fabrics and resulting bloodstains. Forensic Science International, 327, 112550. https://doi.org/10.1016/j.forsciint.2021.112550
- The study led by Fujun Wang, focusing on the impact of high-velocity blood spatter on different cotton fabrics, found that the 'fingers' of the blood stain, thin tendrils that spread out from the center of the stain, correlate with the velocity of the blood spatter, providing additional information for forensic investigations.
- The research, published in Forensic Science International, also developed empirical power-law-based models to predict wicking kinematics, the splashing threshold, and the number of satellite droplets during splashing, demonstrating the model's adequacy in describing wicking kinematics.
- Understanding how blood impacts different cotton weaves can significantly assist forensic investigators in reconstructing crime scenes by better estimating the velocity of blood spatter and movement, which is essential for accurate event reconstruction.
- The researchers are planning to further improve forensic bloodstain pattern analysis by conducting additional work with a wider variety of fabrics, weaves, and yarns, with the National Institute of Justice under grant 2018-R2-CX-0033 supporting this study.
