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.