In bloodstain pattern analysis, it is important to know the point of origin (PO) of an impact pattern. This point can be estimated by means of the stringing method, the tangent method, or by commercially available computer programs. In this study, the accuracy of two computer programs was investigated under different conditions. Impact patterns were created by means of a modified mouse trap, and subsequently the PO was calculated. By examining the characteristics of single bloodstains, the influence on the deviation could be determined. To improve the estimation of the PO, it is important to select bloodstains that lie close to the presumable location of the blood source, that are large (width greater than 1.5 mm) and that show an elliptical form. If possible, bloodstains from different walls should be taken into account. The authors' recommendations may improve the PO determination of impact patterns. (Publisher Abstract)