TY - JOUR
T1 - Determining the region of origin of blood spatter patterns considering fluid dynamics and statistical uncertainties
AU - Attinger, Daniel
AU - Comiskey, Patrick M.
AU - Yarin, Alexander L.
AU - Brabanter, Kris De
N1 - Funding Information:
The authors acknowledge financial support from the US National Institute of Justice (Award No. NIJ 2014-DN-BX-K036). This work was also partially funded by the Center for Statistics and Applications in Forensic Evidence (CSAFE) through Cooperative Agreement No. 70NANB15H176 between NIST and Iowa State University, which includes activities carried out at Carnegie Mellon University, University of California Irvine, and University of Virginia. We acknowledge the contribution of Prashant Agrawal, John Polansky and Zaki Jubery in specific aspects of the numerical implementation; useful discussions with Craig Moore; as well as the participants from the Swiss scientific police force to a workshop on the fluid dynamics of BPA in summer 2016 for reconstruction of spatters in Fig. 7 .
Publisher Copyright:
© 2019
PY - 2019/5
Y1 - 2019/5
N2 - Trajectory reconstruction in bloodstain pattern analysis is currently performed by assuming that blood drop trajectories are straight along directions inferred from stain inspection. Recently, several attempts have been made at reconstructing ballistic trajectories backwards, considering the effects of gravity and drag forces. Here, we propose a method to reconstruct the region of origin of impact blood spatter patterns that considers fluid dynamics and statistical uncertainties. The fluid dynamics relies on defining for each stain a range of physically possible trajectories, based on known physics of how drops deform, both in flight and upon slanted impact. Statistical uncertainties are estimated and propagated along the calculations, and a probabilistic approach is used to determine the region of origin as a volume most compatible with the backward trajectories. A publicly available data set of impact spatter patterns on a vertical wall with various impactor velocities and distances to target is used to test the model and evaluate its robustness, precision, and accuracy. Results show that the proposed method allows reconstruction of bloodletting events with distances between the wall and blood source larger than ∼1 m. The uncertainty of the method is determined, and its dependency on the distance between the blood source and the wall is characterized. Causes of error and uncertainty are discussed. The proposed method allows the consideration of stains indicating impact velocities that point downwards, which are typically not used for determining the height of the origin. Based on the proposed method, two practical recommendations on crime scene documentation are drawn.
AB - Trajectory reconstruction in bloodstain pattern analysis is currently performed by assuming that blood drop trajectories are straight along directions inferred from stain inspection. Recently, several attempts have been made at reconstructing ballistic trajectories backwards, considering the effects of gravity and drag forces. Here, we propose a method to reconstruct the region of origin of impact blood spatter patterns that considers fluid dynamics and statistical uncertainties. The fluid dynamics relies on defining for each stain a range of physically possible trajectories, based on known physics of how drops deform, both in flight and upon slanted impact. Statistical uncertainties are estimated and propagated along the calculations, and a probabilistic approach is used to determine the region of origin as a volume most compatible with the backward trajectories. A publicly available data set of impact spatter patterns on a vertical wall with various impactor velocities and distances to target is used to test the model and evaluate its robustness, precision, and accuracy. Results show that the proposed method allows reconstruction of bloodletting events with distances between the wall and blood source larger than ∼1 m. The uncertainty of the method is determined, and its dependency on the distance between the blood source and the wall is characterized. Causes of error and uncertainty are discussed. The proposed method allows the consideration of stains indicating impact velocities that point downwards, which are typically not used for determining the height of the origin. Based on the proposed method, two practical recommendations on crime scene documentation are drawn.
KW - Ballistic
KW - Bloodstain pattern analysis
KW - Fluid dynamics
KW - Probabilities
KW - Reconstruction
KW - Uncertainty propagation
UR - http://www.scopus.com/inward/record.url?scp=85062914206&partnerID=8YFLogxK
U2 - 10.1016/j.forsciint.2019.02.003
DO - 10.1016/j.forsciint.2019.02.003
M3 - Article
C2 - 30974388
AN - SCOPUS:85062914206
SN - 0379-0738
VL - 298
SP - 323
EP - 331
JO - Forensic Science International
JF - Forensic Science International
ER -