Bloodstain Pattern Analysis (BPA)
Definition
The scientific discipline that examines the size, shape, distribution, and location of bloodstains to reconstruct the events that produced them, addressing questions of force, direction, and sequence.
- Discipline
- Crime scene reconstruction from bloodstain evidence
- Examines
- Size, shape, distribution, and location of bloodstains
- Answers questions of
- Force, direction, and sequence of events
- Core physics
- Droplet trajectory and surface impact geometry
Common questions
How does stain shape reveal the direction a blood drop travelled?+
A blood drop striking a surface at an angle produces an elongated, tadpole-like stain with the tail pointing in the direction of travel, while a drop striking perpendicular to the surface produces a more circular stain. Measuring the length-to-width ratio of the stain lets an analyst calculate the impact angle.
What distinguishes impact spatter from other bloodstain pattern categories?+
Impact spatter results from a force striking a blood source, such as a blow or gunshot, dispersing many small droplets outward, in contrast to passive drops that fall under gravity alone or transfer stains left when a bloody object contacts a surface. Distinguishing these categories is central to reconstructing what kind of event produced the scene.
Related terms
- IABPA
- The International Association of Bloodstain Pattern Analysts, founded 1983, which sets training standards and accreditation criteria for BPA specialists.
- Passive Drip
- A stain formed when blood falls from a source under gravity alone. The resulting drop is roughly circular; its diameter correlates with...
- Presumptive Test
- A fast, low-cost, class-specific screen used to triage a caseload before instrumental work begins. Examples are Marquis reagent for opioids and amphetamines,...
- Projected Pattern
- A pattern produced when blood is expelled under pressure or force exceeding gravity, as in arterial spurting, impact spatter, or cast-off from...
- Transfer Stain
- A stain deposited when a wet, blood-bearing object contacts a surface and leaves an impression. Shoe soles, hands, fabric, and tools can...