Errors in the determination of the point of origin of bloodstains

Bloodstain pattern analysts are sometimes called upon to determine the point of origin of a pattern of bloodstains. A derivation of expressions for the uncertainties δX and δY in the coordinates of the point of origin P(X, Y) of two bloodstains on a surface has recently been published. These uncertainties were expressed in terms of the uncertainties in the measured distance between the bloodstains and the uncertainties in the angles of impact of the bloodstains. This paper extends the derivations in the previous work by expressing the uncertainties in the coordinates of the point of origin of two bloodstains in terms of the uncertainties in the length and width measurements from which the angles of impact of the bloodstains are calculated.