The use of small bloodstains in blood source area of origin determinations

Due to the increased likelihood of manual measurement error, small bloodstains (≤ 3.0mm long) have rarely been used in three-dimensional blood source area of origin determinations. The advent of computer assisted measurement methods, offering improved levels of accuracy and precision, broadens the range of bloodstain sizes available for selection to determine a blood source area of origin. With inertia, viscosity and surface tension playing important, yet competing, roles in bloodstain formation, the power law relationships that exist between droplet volumes, droplet diameter, and bloodstain width suggest possible non-agreement between experimentally calculated angle of impact values when compared against those values theoretically expected. In order to compare experimental angle of impact calculation trends with angle of impact calculation theory, this preliminary study examines small bloodstains created by blood drops falling vertically onto surfaces offset from the vertical and small bloodstains generated by impact events subsequently deposited on adjacent vertical surfaces. This study shows that an apparent power law relationship may exist between the size of a parent blood droplet and the role of viscous and surface tension forces on subsequent bloodstain formation, particularly on those bloodstains caused by small droplets impacting obliquely with planar surfaces.