Oscillating blood droplets--implications for crime scene reconstruction.

Traditionally, the analysis of blood spatter on surfaces in the reconstruction of crime scenes relies on the assumption that blood droplets are spherical when they strike the surface. This paper explores the effects of their shape on the reconstruction of trajectories from their impact pattern, and reports a theoretical analysis of the lifetime of droplet oscillations. Oscillations damp quickly in blood droplets due to the viscosity. The analysis provides ranges of velocities and distances from the point of droplet projection within which it is unreliable to assume the droplets are spherical when they stain a surface. Non-spherical droplet stains predict incorrect positioning of the droplet projection point. Experimental data are presented to show that the estimates apply in practice.