CFC Bloodstain Pattern Analysis 4 — Questions and Answers
Question 1: Which factor does NOT directly affect the size of a blood droplet in free fall?
- Surface tension of blood
- Viscosity of blood
- Air temperature at the scene
- Ambient humidity (Correct answer)
Correct answer: Ambient humidity
Ambient humidity does not directly affect droplet size during free fall; surface tension and viscosity are the primary physical properties that determine blood droplet size.
Question 2: A curved cast-off pattern on a wall most directly indicates:
- The victim was dragged across the room
- A bloody object was swung in an arc, releasing blood during the backswing or follow-through (Correct answer)
- Blood was propelled by arterial pressure
- The perpetrator wiped a weapon on the wall
Correct answer: A bloody object was swung in an arc, releasing blood during the backswing or follow-through
Cast-off patterns result from blood being flung from a moving bloody object (such as a weapon being swung), and the arc shape reflects the path of that swing.
Question 3: In BPA, what is the significance of multiple parallel cast-off stripes on a ceiling?
- They indicate a single, powerful blow was delivered
- They indicate the weapon was swung multiple times, with each stripe representing one swing (Correct answer)
- They demonstrate the victim moved during the assault
- They are characteristic of arterial spurting against an overhead surface
Correct answer: They indicate the weapon was swung multiple times, with each stripe representing one swing
Each arc stripe in a cast-off pattern on a ceiling typically represents a separate swing of the bloody object, allowing analysts to estimate the minimum number of blows.
Question 4: Which type of transfer stain would be most useful in identifying a specific tool or object used at a crime scene?
- Pool
- Smear
- Pattern transfer (contact stain) (Correct answer)
- Satellite spatter
Correct answer: Pattern transfer (contact stain)
A pattern transfer or contact stain preserves the shape of the object that created it, potentially matching a specific tool, hand, shoe, or fabric pattern.
Question 5: When blood drops fall from a greater height onto a horizontal surface, the resulting stain will:
- Be smaller with smoother edges
- Be larger with more pronounced scalloping and satellite spatter (Correct answer)
- Have more elongation due to increased horizontal velocity
- Remain unchanged in size regardless of height
Correct answer: Be larger with more pronounced scalloping and satellite spatter
Greater fall height increases droplet velocity, producing a larger stain upon impact with more pronounced scalloping and satellite spatter due to higher kinetic energy.
Question 6: What does a 'flow pattern' in BPA primarily reveal about an event?
- The number of wounds sustained by the victim
- The direction of gravity or the position/orientation of a bleeding surface (Correct answer)
- The force used in an assault
- The time elapsed since the blood was deposited
Correct answer: The direction of gravity or the position/orientation of a bleeding surface
Flow patterns result from blood moving under gravity, revealing the orientation of the surface (or body) at the time of bleeding and helping establish body position.
Question 7: The IABPA (International Association of Bloodstain Pattern Analysts) recommends that analysts use which framework when reporting findings?
- Absolute conclusions based on pattern type alone
- A linear certainty scale from 'impossible' to 'certain'
- Terminology that reflects the probabilistic nature of BPA conclusions (Correct answer)
- Qualitative descriptions without referencing probability
Correct answer: Terminology that reflects the probabilistic nature of BPA conclusions
IABPA guidelines emphasize using terminology that accurately reflects the probabilistic and interpretive nature of BPA, avoiding overstatement of certainty.
CFC Bloodstain Pattern Analysis 4
Which factor does NOT directly affect the size of a blood droplet in free fall?