DETERMINING POINT-OF-ORIGIN
Although it may seem a macabre game of connect-the-dots, determining the point-of-origin of one or more bloodstains is central to the reconstruction of a blood-related event. Whenever the direction of a bloodstain can be determined, it can be expected to have originated at a point somewhere along that line. Doing this for a number of bloodstains can demonstrate a convergence of lines (paths), indicating a possible point-of-origin for the stains, as shown in Figure 10.8. The more paths converge to this point, the more confidence the analyst has in that point being the origin of the pattern . The analyst must be aware that multiple paths may cross, generating a confusing or conflicting pattern . A bloodstain scene may be particularly difficult to interpret. Visual aids, from simple strings and pins to advanced forensic software, are available to assist the analyst. Stringing a scene, depicted in Figure 1, is the easiest and cheapest method to interpret multiple bloodstain patterns. The path of a bloodstain is established, and a string is run from that point backward using pushpins or masking tape to fasten the ends; this process is repeated for numerous stains until the pattern’s origin becomes clear. Rulers, protractors, and even laser pointers can be used in this method. Software, such as Backtrack/Images and Backtrack/Win, available through Forensic Computing of Ottawa (www.physics.carleton.ca/∼carter/index.html), can assist through the automated calculation of vectors and angles; an example is shown in Figure 10.10.
FIGURE 1 The easiest and cheapest method of interpreting bloodstain patterns is stringing. A string is run from the presumptive source to the target, using pushpins or masking tape to fasten the ends. Rulers, protractors, and even laser pointers can be used in this method.
