Blood Stain Pattern Analysis Notes

Understand and define key terms relevant to blood stain pattern analysis.
Examine the effects of surface texture, directionality, and angle of impact on bloodstain shapes.
Calculate the angle of impact using bloodstain dimensions.
Describe classifications of low, medium, and high-velocity impact spatter.
Discuss methods to determine area of convergence and area of origin for impact spatter patterns.
Review the creation of various blood pattern types and their features relevant to crime scene reconstruction.
Describe methods for documenting bloodstain patterns at a crime scene.

Definition: The method used to establish a series of possible events through examination and interpretation of physical evidence and statements.
Process:
- Determining sequence of events related to what happened before and after a crime.
- Replication of crime scene through study and interpretation of scene patterns.
- Evaluation of physical evidence, including photographs, measurements, and sketches.
Requirements: All photographs, physical evidence, notes, measurements, and sketches must be obtained, ensuring thorough reconstruction depends on comprehensive information.
Experts Involved: Collaboration between forensic experts, criminalists, and law enforcement personnel is critical.
Example: Using a laser beam to establish bullet path from a sniper shot through a window by lining up the victim's bullet wound with the bullet hole.

Context: Bloodstain patterns from violent interactions provide valuable information about the events that occurred during a crime.
Types of Information Revealed:
- Direction from which blood originated.
- Angle at which droplets struck surfaces.
- Location of the victim during bloodshed.
- Movement of a bleeding individual.
- Approximate number of blows struck.
- Estimated location of the individual delivering blows.

Key Concept: Surface texture influences the size, shape, and spattering level of blood stains.
General Rule: Harder and less porous surfaces produce less spatter.
Figures:
- Figure 4–2a: Bloodstain from a single drop on glass surface.
- Figure 4–2b: Bloodstain from a single drop on cotton muslin.

Concept: Impact spatter results from an object impacting a blood source.
Types of Spatter:
- Forward Spatter: Projects outward from the source.
- Back Spatter (or blow-back spatter): Projects backward from the source.
Classification by Velocity:
- Low Velocity Spatter: Drops >4 mm in diameter, caused by applied force <= 5 ft/sec.
- Medium Velocity Spatter: Drops between 1-4 mm in diameter, caused by applied force 5 to 25 ft/sec.
- High Velocity Spatter: Drops <1 mm in diameter, caused by applied force >= 100 ft/sec.

Definition: The area where blood drops converge on a two-dimensional plane to trace the origin of blood in an impact pattern.
Process: Establishing area of convergence by drawing straight lines through the long axis of bloodstains, following the tails.

Definition: The three-dimensional space where blood was projected and the location of the event causing the stains.
Method: The string method—approximates the area using angles of impact from stains in the pattern.

Importance: Accurate documentation is essential for later interpretation and courtroom presentation.
Methods:
- Grid Method: Setting up a grid of known dimensions over the blood pattern.
- Perimeter Rule Method: Setting up a rectangular border of rulers around the pattern with smaller rulers beside each stain.