The Physics of Blood Spatter

Introduction

• Bloodstain pattern analysis (BPA) is crucial for crime scene investigation, especially in shootings.
• Recent critiques question the scientific rigor and accreditation of BPA, leading to calls for reassessment.
• The case of Joe Bryan, convicted based on BPA evidence, highlights potential flaws in the technique.

Historical Context

• BPA has roots in late 19th-century Europe and gained prominence in the US with the 1955 Sam Sheppard trial.
• It has been used in notable trials like O.J. Simpson and Phil Spector.

Challenges in Bloodstain Pattern Analysis

• BPA involves fluid mechanics, considering blood's liquid (plasma) and solid (cells) components.
• Blood properties vary between individuals, complicating analysis.
• BPA lacks strict educational requirements, leading to subjective interpretations.
• The 2009 US NAS report criticized BPA for lacking scientific rigor.

Scientific Approaches to BPA

Improvements in Analysis

• Geometry of Spatter: Blood droplets create elliptical stains, traditionally analyzed via straight-line trajectories.
  • This overestimates the height of wounds due to gravitational and aerodynamic effects.
• Varney & Gittes (2011): Developed equations incorporating gravity and drag to improve height estimation.
• Laan et al. (2015): Used blood's fluid dynamics to better estimate gunshot wound height.

Bullet Trajectory and Spatter Analysis

• Yarin, Comiskey, & Attinger: Modeled the entire bullet-to-bloodstain process.
  • Analyzed back and forward spatter using fluid dynamics and percolation theory.
  • Studies showed agreement with experimental data but indicated need for further research.

Practical Implications and Developments

• BPA requires translation into practical forensic and courtroom procedures.
• Resistance from practitioners to change established methods.
• Efforts underway to bridge the gap between BPA and fluid dynamics.
  • Carriquiry and CSAFE involved in fostering scientific partnerships.

Laboratory and Field Research

• Attinger's Team: Created controlled blood spatter patterns for study and training.
  • Developed tools and visual aids to support BPA practice.

Conclusion

• Adoption of rigorous BPA methods will take time and won't immediately rectify past errors.
• Ongoing efforts aim to improve the scientific basis of BPA to ensure accurate and just legal outcomes.
• Highlighting cases like Joe Bryan’s emphasizes the need for scientifically sound BPA methods in justice.