3D laser scanning technology : calculating the area of origin for bloodstains using FARO Zone 3D.

Abstract

Bloodstain pattern analysis possesses a subjective nature in the calculation of are of origin and has inherently received criticism in the scientific community. Current software used in analyzing area of origin (AO) for medium energy spatter stains does not account for alteration during formation of the stains across different target mediums. This calls into question the validity and reliability of the methods used in evaluating bloodstain patterns. Previous literature of bloodstain pattern analysis has examined different software and compared the results of AO calculation to one another and to a known point of origin. The majority of this analysis has been conducted by Eugene Liscio in correlation with other associates in the BPA community. The methodology has usually consisted of single planar target surfaces of a homogeneous material. A few studies have used surfaces along different axes and curved surfaces for analysis, again with homogeneous material. The results of previous research has validated the software that was being tested by providing measurements of the calculated AO within an acceptable statistical variability of the known point of origin. The current thesis research consists of two parts, the first is a validation of the software for a bloodstain on a single planar surface, while the second is for a bloodstain deposited across multiple target mediums of perpendicular planes. The thesis statements for each are as follows: Validation: H0: When a medium energy impact bloodstain pattern is analyzed using Faro Zone 3D to determine area of origin, there will be no significant statistical variance of measurement along the x, y, and z axes compared to the known point of origin. Multiple Mediums: H0: When using Faro Zone 3D to analyze and determine the area of origin for a single source, medium energy impact spatter pattern, there will be no significant statistical variance of measurement along the x, y, and z axes compared to the known point of origin. The present research methodology is analysis of quantitative data with measurements and statistical analysis being compared to determine validity. Based on the results for bloodstain pattern one, it is clear that the software lacks validity when analyzing this type of single directionality bloodstain. The less than accurate results are based on the large displacement value for the x-axis. The y and z-axis displacement values are within an acceptable variance based on the 7-cm boundary explained by Dubyk and Liscio (2016), stating that measurement is about the average size of a human skull. The x-axis produced the greatest amount of variability for bloodstain pattern 1 because the area of origin could not be triangulated with analyzed stains on the opposite side of where the spatter originated from along the planar target medium. This triangulation effect is what controls the accuracy of the x-axis coordinate. The y-axis is controlled by the elliptical overlay of each individual stain for which the angle of impact is calculated with the Balthazard Formula. The z- axis is primarily sourced from the stains selected as suitable for analysis and their angle of convergence along a two-dimensional surface. While the validity of Bloodstain Pattern 1 was less than reassuring, Bloodstain Pattern 2 exemplified much more confident results of validity based on the Dubyk and Liscio defined acceptable variance. However, based on the statistical analysis of a 95% confidence interval for each of the bloodstain patterns, neither AO analysis by FARO Zone 3D met the intervals of validity for all axes. In fact, Bloodstain Pattern 1 did not have any of the axes displacement measurements for the AO sphere fall within the range produced by the confidence interval. Bloodstain Pattern 2 did produce an accurate analysis along the z-axis, but both the x and y-axis measurements were outside the acceptable confidence ranges. Therefore, the analytical research rejects the null hypothesis of validity. The findings of this research reject validity in the science of bloodstain pattern analysis by limiting the subjective nature of analysis by using software that calculates the area of origin for medium energy spatter stains. The results also show that bloodstains deposited across multiple target mediums are capable of being analyzed as a single source stain and the alteration of stain formation does not impact the AO calculation enough to be statistically significant. An additional aspect of the FARO Zone 3D software is the ability to reproduce a two-dimensional sketch that is to scale of a scene with the BPA analysis visible, as well as a digital three-dimensional representation of the scene. As instances of BPA are often used in court to assist in interpretation of the facts, visual representation is an important so full understanding during testimony can be achieved.