In-Depth Notes on Bloodstain Pattern Analysis

Introduction to Bloodstain Pattern Analysis (BPA)

  • Presented by Ted Selineks: Retired forensic scientist from Forensic Science Centre of South Australia.
  • Role: Bloodstain pattern analyst focusing on bloodstain evidence from crime scenes.
  • Viewer Advisory: Includes graphic content related to bloodstains and crime scenes; viewer discretion is advised.

Overview of Bloodstain Pattern Analysis

  • Definition: Examination of bloodstain characteristics, including size, shape, and distribution at a crime scene.
  • Scientific Foundations: Involves physics, mathematics, and biology, alongside anatomy and fluid dynamics.
  • Purpose: Provides information on the sequence of events, perpetrator movements, and type of violence encountered.

Importance of Blood in Forensic Science

  • Properties of Blood:

    • Composed of 45% red blood cells, 55% plasma; erythrocytes lack nuclei, hence no DNA.
    • Heme molecule is key in screening tests for blood.
    • Blood is influenced by cohesive properties (surface tension) when in motion.

  • Blood Volume: Average male has approximately 5 liters of blood circulating.

  • Physiological Responses: Heart rate increases (e.g., 50 beats per minute during stress), affecting blood loss and patterns recorded.

Screening Tests for Blood

  • Sensitivity vs. Specificity: Most screening tests react to multiple substances, not solely blood.
  • Common Tests:
    • Hemosix and Castle Mire Tests: Used for initial screening, with noted limitations and maintenance needs.
    • Confirmatory Tests: Navicar Hematrace test uses antibodies to confirm human hemoglobin.
  • Blood Enhancements: Techniques to visualize latent blood stains through chemiluminescence or alternate light sources like luminal and amido black.

Bloodstain Behavior and Types

  • Mechanics of Blood Drops: Blood droplets behave predictably under the laws of physics; spatter can yield evidence about the source and type of impacts.
  • Categories of Bloodstains:
    • Passive Stains: Formed by gravity alone (e.g., drips or flows).
    • Spatter Stains: Created by additional forces; can indicate the use of weapons.
    • Transfer Stains: Result from contact between surfaces.
    • Altered Stains: Show changes due to dilution or environmental factors post-incident.

Impact Spatter and Reconstructive Analysis

  • Impact Spatter: Notable for their size and distribution, affected by the force applied; can show directionality and point of origin.
  • Angle of Impact: Determined using the ratio of width to length of bloodstains through trigonometric calculations (e.g., sine rule).
  • Methodologies: Bloodstains can be physically measured and visualized through advanced technologies, including computer aid and manual stringing of stains back to points of convergence.

Analysis of Clothing Evidence

  • Challenges in Textile Analysis: Clothing absorbs blood differently; must consider how blood moves on curved surfaces vs. flat.
  • Three-Dimensional Reconstruction: Using controlled environments for better accuracy in placing the patterns.
  • Case Examples: Situations depicted where bloodstains on clothing indicate positions of individuals during the events leading to bloodshed.

Conclusion and Further Questions

  • Q&A Invitation: Encourages engagement for additional information or clarifications via email.