Lecture on Blood Spatter Analysis

Introduction to Blood Spatter

• Blood spatter analysis (BSPA) involves studying patterns of blood stains on surfaces.
• Helps determine:
  • Type of weapon used
  • Speed of the weapon
  • Number of blows
  • Assailant's handedness and position
  • Sequence of wounds
  • Movement of the assailant
  • Type of injuries
  • Timing of death (immediate or delayed)

Forensic Detection Techniques

• Light Sources: Use UV lights and special filters to make blood visible.
• Presumptive Tests: React with hemoglobin properties but don't confirm if blood is human.
  • Examples include phenolphthalein and heme sticks.
• Luminol: Sprayed to detect blood; glows blue in darkness.
  • Reacts to cleaned areas, especially with bleach.
• Fluorescein: Glows greenish-white for fine stains; reacts with copper and bleach.
• Crystal Violet/Leukocrystal Violet: Used for photographing; turns purple/violet.

Types of Blood Spatter Patterns

• Passive: Result of gravity (drops, flows, pools).
• Projected: Force applied; categorized as low, medium, or high velocity.
• Transfer/Contact: Weapon or person contacts surface, leaving a pattern.

Blood Stain Characteristics

• Shape and Size: Indicates random distribution; helps locate crime scene.
• Stringing and Lasers: Techniques for determining position and force.
• Spines and Satellites:
  • Spines: Radiate from the parent drop; affected by height and surface.
  • Satellites: Small drops that break away.

Physics of Blood Drops

• Speed and Diameter: Faster drops have larger diameters; affected by height.
• Surface Type:
  • Smooth surfaces (e.g., glass) result in clean lines.
  • Rough surfaces (e.g., wood) cause more spines.
  • Carpet absorbs drops, complicating analysis.

Determining Direction and Angle

• Directionality: Elongated stains indicate direction; "tail tells the tale."
• Angle of Impact: Trigonometry used to calculate using width and length.
  • Excel spreadsheets can automate calculations.
• Point of Convergence/Origin:
  • Point of Convergence: Lines drawn through drops converge to indicate source.
  • Area of Origin: Multi-dimensional analysis (x, y, z-axes) to pinpoint source.

Lab Activities

• Practical exercises will involve stringing techniques and use of technology like lasers.
• Measurements and calculations will be guided by provided software tools.