Bloodstain Pattern Analysis

Bloodstain Pattern Analysis Overview

  • Key Concepts: Understanding bloodstain patterns is crucial for crime scene investigation as they provide critical insights into the sequence of events during a violent crime.

General Bloodstain Features

  • Importance of Bloodstains:

    • Bloodstains on various surfaces (floors, walls, bedding) can reveal important details about the violent events that took place.
    • Analysis involves considering the location, distribution, and appearance of bloodstains.

  • Interpretative Clues:

    • Direction from which blood originated.
    • Angle of impact and the position of the victim during injury.
    • Movement of the victim and the approximate number of blows inflicted.

Effects of Surface Texture

  • Surface texture affects bloodstain characteristics:

    • Hard surfaces: Create less spatter.
    • Porous surfaces: May absorb blood and affect stain appearance.

  • Important Factors:

    • Shape, size, and location of stains help determine the direction and impact angle.

Directionality and Angle of Impact

  • Bloodstain Direction:

    • The pointed end of a stain indicates the direction of travel.
    • The impact angle affects the stain's shape; horizontal impacts create circular stains, while oblique impacts result in elongated shapes.

  • Calculating the Angle of Impact:

    • Use the equation: ext{Sin}^{-1}(A) = rac{ ext{Width of blood stain}}{ ext{Length of blood stain}}

Types of Impact Bloodstain Patterns

  • Spatter Stains: Result from blood drops dispersed through the air.
  • Forward Spatter: Flows in the same direction as the force.
  • Back Spatter: Flows opposite to the force, often seen in entrance wounds from projectiles.

Classifying Spatter Patterns

  • Patterns can be classified based on droplet size and velocity, such as low, medium, and high-velocity spatter. However, these classifications are not standardized by SWGSTAIN.

Sources of Bloodstain Patterns

  • Spatter Stains: Created by object impacting blood (impact pattern).
  • Cast-off Patterns: Blood released from a moving, blood-covered object.
  • Projected Patterns: Blood released under pressure (e.g., arterial spurting).

Area of Convergence and Area of Origin

  • Area of Convergence: The point of origin of stains can be determined on a two-dimensional plane by tracing the long axes of stains.
  • Area of Origin: Determines the three-dimensional space from which blood was projected, indicating the positions of individuals at the crime scene.

Gunshot Bloodstains

  • Gunshots can create distinctive patterns:

    • Exit wounds cause forward spatter.
    • Entrance wounds cause back spatter.

  • Distance Matters: The distance from which a gun is fired can affect spatter patterns on the shooter.

Specialized Bloodstain Patterns

  • Transfer Stains: Result from blood contact between surfaces.
  • Swipe Patterns: Indicate motion from a blood-bearing surface.
  • Wipe Patterns: Result from movement through a pre-existing bloodstain.

Flow Patterns and Pools

  • Flow Patterns: Result from blood movement due to gravity or the movement of objects/bodies.
  • Pools: Accumulated blood creates larger patterns, which can indicate timing and actions based on drying times and environmental factors.

Edge Characteristics and Perimeter Stains

  • Edge Characteristics: Involves the physical features of stain edges, including skeletonization.
  • Perimeter Stains: Altered stains indicative of contact and can help recreate event sequences.

Drip Patterns and Trails

  • Drip Trails: Series of drops indicating motion from a source, can provide clues about movement and actions post-injury.
    • Types: Includes drip patterns, drip stains, and drip trails.

Documenting Bloodstain Evidence

  • Proper documentation techniques:

    1. Grid Method: Overlay a grid for precise measurements.
    2. Perimeter Ruler Method: Establish a ruler layout around patterns for scale in photographs.

  • New technologies (e.g., laser scans) enhance crime scene reconstruction.

Interpretation of Bloodstain Evidence

  • Importance of familiarity with bloodstain patterns among investigators for accurate documentation and reconstruction of crime events.