1. Determination of the Impact angle and directionality of a bloodstain

2. A diagram of a collapsing droplet impacting at an acute angle. This demonstrates how the long axis of the ellipse develops and is oriented along the path of travel. Unless impacting at 90°, the axis associated with the direction of travel is always longer as a result of the skimming action of the droplet on the target. (Bevel and Gardner, 2002)

4. The presence of spines, scallops, spatter, or tails help the analyst identify the path the droplet was traveling at impact. These structures are found opposite (or at least are concentrated opposite) the side of the stain that impacted first. (Bevel and Gardner, 2002)

5. (Bevel and Gardner, 2002) A 90° impact. Small scallops appear around the entire periphery of the stain. A 70° impact. Note the greater concentration of large scallops on one side of the stain. They are opposite the droplet’s origin and point in the general direction the droplet was travelling. Directionality in circular stains is not as clear as in elliptical stains because the spines are not concentrated along a single vector.

6. (Bevel and Gardner, 2002) A 50° impact. In this instance the scallops have spawned significant tadpole tails. Once again the tails align with the long axis of the stain and point in the direction the droplet was travelling. Although directionality is not as specific as when we find a single tail, the analyst can clearly define the droplet’s directionality. A 20° impact. This stain has a tail and detached satellite. In combination with the long axis of the elliptically shaped stain, it provides a very specific indication of the droplet’s path of travel.

7. Results from previous work 15º Impact on Office Paper 40º Impact on Office Paper

8. Sin θ = opp (A) (or B to A) so Sin θ = width hyp (C) (or B to C) length

9. By accurately measuring the length and width of a bloodstain, the impact angle can be calculated using the SIN formula below e.g. length 3.0 cm width 1.5 cm Sin θ = opp (A) (or B to A) so Sin θ = width hyp (C) (or B to C) length For the exemplar figures above: Sin θ = 1.5cm/3.0cm so Sin θ = 0.5 using the inverse of SIN we get 30º

10. References Jackson R W and Jackson J (2004). Forensic Science. Pierson. Bevel T and Gardner R M (2002). Bloodstain Pattern Analysis (2 nd Edition). CRC Press. Slemko J (2005). Bloodstain pattern Analysis Tutorial. http://www.bloodspatter.com/BPATutorial.htm page last accessed 7th February 2009