CFC Bloodstain Pattern Analysis 5 — Questions and Answers
Question 1: Presumptive testing for blood at a crime scene using luminol is most limited by which factor?
- It destroys all DNA evidence in tested areas
- It can produce false positives with certain chemicals such as bleach or plant peroxidases (Correct answer)
- It only reacts with dried blood older than 24 hours
- It requires ultraviolet light to activate the reaction
Correct answer: It can produce false positives with certain chemicals such as bleach or plant peroxidases
Luminol is a presumptive test that can produce false positives with oxidizing agents like bleach, copper compounds, and plant peroxidases, requiring confirmatory testing.
Question 2: Which scenario would most likely produce a 'projected spatter' pattern rather than impact spatter?
- A hammer blow to a bloodied head
- Blood dripping from a wound to the floor
- Blood spurting from a severed artery under cardiac pressure (Correct answer)
- A body falling onto a hard surface
Correct answer: Blood spurting from a severed artery under cardiac pressure
Projected spatter results from blood being propelled under internal pressure (e.g., arterial pressure from the heart), not from an external force striking a blood source.
Question 3: A forensic consultant interpreting a bloodstain pattern should give most weight to:
- The investigator's initial theory of the case
- The totality of physical evidence and scene context (Correct answer)
- The pattern type that is most dramatic or unusual
- Witness statements about what occurred
Correct answer: The totality of physical evidence and scene context
Sound BPA interpretation requires integrating all physical evidence and scene context rather than conforming to a predetermined theory or relying solely on one category of evidence.
Question 4: In a scene where blood is found on both the ceiling and floor, but not on nearby walls, the analyst should consider:
- A medium-velocity impact from a weapon swing
- Arterial gushing directed upward followed by pooling (Correct answer)
- That the walls were cleaned post-event
- A projected spatter from a pressurized container
Correct answer: Arterial gushing directed upward followed by pooling
Blood on the ceiling and floor without wall staining could suggest upward arterial spurting that reached the ceiling, with gravity returning blood to the floor, though other hypotheses should be evaluated.
Question 5: When calculating the angle of impact of a bloodstain, the analyst uses the formula arcsin(width/length). If the width is 8mm and the length is 16mm, the impact angle is approximately:
- 15 degrees
- 30 degrees (Correct answer)
- 45 degrees
- 60 degrees
Correct answer: 30 degrees
Arcsin(8/16) = arcsin(0.5) = 30 degrees, meaning the droplet struck the surface at approximately 30 degrees from the surface plane.
Question 6: Which characteristic of a bloodstain tail (satellite or wave cast-off) most reliably indicates the direction of travel of the blood droplet?
- The tail or spines point in the direction of travel (Correct answer)
- The scalloping is most pronounced at the leading edge
- The stain is narrower at the point of impact than at the tail
- The satellite drops are larger in the direction opposite to travel
Correct answer: The tail or spines point in the direction of travel
The tail or spines of an elongated bloodstain point in the direction of the droplet's travel, allowing analysts to determine the direction from which blood came.
Question 7: A CFC candidate reviewing a case notes that the defense claims blood was tracked into a room on a shoe after the incident. Which type of evidence would best support or refute this claim?
- The color of the blood (bright red vs. dark)
- Shoe print transfer patterns with tread morphology and blood concentration gradients (Correct answer)
- The victim's blood type alone
- The presence of clotting in the tracked stains
Correct answer: Shoe print transfer patterns with tread morphology and blood concentration gradients
Shoe print transfer patterns showing the tread pattern, decreasing blood concentration with successive steps (step-fade), and directionality can confirm or refute the tracked-blood hypothesis.
CFC Bloodstain Pattern Analysis 5
Presumptive testing for blood at a crime scene using luminol is most limited by which factor?