Affect of impact angle variations on area of origin determination in bloodstain pattern analysis

The estimation of the location of the area of origin of a blood source is of major importance within bloodstain pattern analysis. Given this, it is particularly important to establish the accuracy of such estimations. This study examines error rates by investigation of alpha angle inaccuracies of upward directional stains and compares a virtual bloodstain pattern model to real bloodstain patterns. It was found that the size of the area of origin influences the level of accuracy required in alpha angle estimations: larger areas of origin tolerated larger errors. Practical applications of the virtual model using real bloodstain patterns demonstrated that alpha angle measurements may show an inaccuracy of approximately 0° - 12° within a single pattern. The averaging process that occurs in estimating the area of origin lessens the influence of a few large variations, such that, there is no significant change in the area of origin estimation. The virtual model was validated as a conservative indicator, by means of overestimation, of the influence of alpha angle inaccuracy on area of origin. The study confirms that with proper stain selection, straight-line trajectories to estimate area of origin are valid and reliable.