Question

4. How did the appearance of the blood spatter pattern change as the angle of incidence increased from 0° to 80°? How can the determination of the angle of incidence be useful in the analysis of blood spatter patterns? 5. Use your measurements of the major and minor diameters from the Angle of Incidence portion of the exercise to calculate each incident angle. Did the calculated measurements of the incident angle agree with the actual incident angle used? If not, explain some of the reasons why this happened. 6. Based on your experiments, what conclusions can you draw about the accuracy and precision of blood spatter trajectory determinations?

Answer 1

Study of blood spatter patterns play a useful role in forensic science. For investigating a crime scene related with blood patterns one has to have the knowledge of these patterns. The blood spatter pattern change according to the angle of impact (angle of incidence). A blood droplet when freefall under gravity or with minimal force vertically straight downwards (making an angle of 90 degree) it takes a preety much circular shape depending on the type of surface where it falls. This is due to the surface tension of the blood. As the angle of impact decreases the blood stain gradually starts getting elongated (as shown in figure) and the width decreases. Spine like structure appears opposite the angle of impact. These structures further help us in analysing the spatter pattern. Force of impact also plays a crucial role in it.

The angle of impact can be calculated using the width and length of the blood stain.

Inverse of sine (also called Arcsine) of width/length will tell us the angle of impact.

As shown in the figure: Arcsine (y/x) = Angle of impact.

Thus, the determination of angle of incidence is useful in analysis of blood spatter patterns.

blood falling source straight downwards 900 700 50° 200 KY