Interpreting Bloodstain Patterns (lecture 15)

Interpreting Bloodstain Patterns

Dynamic Patterns

  • Blood mass broken into droplets
  • Spatter patterns feature multiple small stains radiating from a central point
  • Individual stain sizes: <1mm to 5mm
  • Types of spatter:
    • Impact spatter (e.g., gunshot, blunt trauma)
    • Expiratory spatter (blood exhaled from airway)

Spatter Pattern Analysis

  • Determines area of origin of the event
  • Identifies possible positions at the crime scene
  • Establishes specifics of the incident (number of events, type of force)
  • Classifies into low, medium, or high velocity

Analyzing Blood Stain Shape

  • Blood droplets project outward when impacted
  • Draw lines through long axis to find point of convergence
  • Consider angles of impact to determine the area of origin

Angle of Impact

  • 90 degrees = circular stain
  • <90 degrees = elliptical stain
  • Measure width and length of stains for better angle approximation using trigonometry

Stringing a Scene

  • Technique to establish 3D origin of bloodstain patterns
  • Use strings and a protractor to trace angles back to where stains converge
  • Helps determine the position of the victim during blood spattering

Cast-Off Patterns

  • Result from a bloodied object being swung or moved
  • Produces stains in straight/curved lines
  • Helpful in assessing the position and orientation of the weapon used

Death Investigations Overview

  • Coroner system: investigates unexpected deaths, historically from English law
  • Responsibilities of coroners include establishing facts of the death
  • Forensic pathologists perform autopsies and work alongside coroners

Coroner Systems and Inquests

  • Coroners are typically medical doctors
  • Jurisdiction includes inquiries into sudden or accidental deaths
  • Inquests help inform the public and improve safety through legislation and policy changes

Postmortem Changes & Indicators of Time Since Death

  • Key indicators: rigor mortis (muscle stiffening), livor mortis (blood pooling), algor mortis (body cooling)
  • Time of death determined through multiple methods
  • Considerations include environmental factors and postmortem changes to narrow timeframe

Conclusion

  • Effective death investigation involves collaborative efforts between coroners, forensic pathologists, and forensic analysis techniques to determine circumstances surrounding a death, including aspects like blood pattern analysis and postmortem changes.