Bloodstain Pattern Analysis Fundamentals
What this domain tests
Bloodstain pattern analysis fundamentals test recognition of passive, transfer, and spatter patterns and the basic geometry used to estimate angles and origins.
Core rules and concepts
- Passive patterns include drops, flows, pools, and saturation.
- Spatter includes impact, cast-off, arterial, and expirated; transfer patterns reflect contact.
- Directionality: the pointed end of an elongated stain indicates travel direction.
- Angle of impact: sin θ = width ÷ length of an elliptical stain.
- Point of convergence is a two-dimensional line; area of origin uses stringing or software to add height.
- Document with scales and orientation; distinguish blood from other red-brown substances with testing.
Worked example
A stain measures 2 mm wide by 4 mm long. sin θ = 2/4 = 0.5, so θ = 30°. A 30° impact angle means the drop struck at a shallow angle, not straight on. Reasoning: the width-to-length ratio gives the sine of the impact angle; ignoring the ratio misclassifies the geometry.
Traps
Overstating what a pattern proves; calling a transfer stain impact spatter; failing to document scale and direction; measuring a stain whose long axis is not clear; assuming blood without a test; ignoring void patterns.