Abstract:
Determining the area of origin of an impact spatter pattern is a critical aspect of bloodstain pattern analysis (BPA) that defines the position of the victim at the time the bloodshed event occurred. A particularly prominent source of error in the BPA process is the manual measurement of bloodstains. More specifically, the elliptical shape of the bloodstain is often overestimated. Recently, three-‐ dimensional (3D) BPA techniques have been developed to incorporate computer-‐based software programmes and laser scan technology. The aim of this thesis was to determine the area of origin uncertainty associated with the FARO Focus3D S 120 laser scanner and the FARO SCENE software. Five impact spatter patterns with known blood source origins were generated. The blood-‐stained surface was scanned and combined with high resolution images to create a 3D virtual environment. Blood droplet trajectories and their probable area of origin were determined using the dimensions and directionality of selected bloodstains. Laser scan settings of 1/4, 1/5 and 1/8, and quality settings of 3x, 4x, and 6x are all acceptable parameters for capturing bloodstain patterns on lightly coloured surface for BPA. The probable area of origin was calculated using five, 10, and 20 stains. All obtained similar results with the exception of an impact spatter pattern that was excluded due to outlier stain selection. Overall, the analysis of 10 stains resulted in average errors and standard deviations of X = 13.65cm ± 6.52cm, Y = 7.73cm ± 4.45cm, and Z = 16.90cm ± 11.99cm. An accurate area of origin was also calculated using only three bloodstain trajectories. The largest error was associated with the Z coordinate; which should be reported as a maximum height estimate. The SCENE Forensic Plug-‐In stain measurement process was compared against alternative manual and computer-‐based measurement methods. The analysis of passive stains and impact spatter pattern stains illustrated that the Forensic Plug-‐In ellipse fitting process is an accurate technique for obtaining bloodstain measurements. The greatest source of error was associated with manual stain selection, not the SCENE workflow. More precise bloodstain origins are likely when the stain selection is conducted by a trained analyst. This study illustrates, that with further development and validation, the FARO Focus3D S 120 and associated software is an accurate and reliable tool for area of origin determinations.