A standard test method of chemical analysis of glass evidence (ASTM E2927-16a) describes a consensus-based approach to sampling, sample preparation, multivariate quantitative elemental analysis and also suggests a “match” criterion for the comparison of chemical properties of glass evidence. The result of the application of the method is a binary decision of either finding a difference in the elemental composition (exclusion) or a failure to exclude, based on elemental composition. This presentation aims to improve on this conclusion by demonstrating the utility of likelihood ratio (LR) calculations using novel datasets of glass samples. Likelihood ratios were calculated using a previously reported multivariate kernel density (MVK) and calibrated with pool adjacent violators (PAV) by the authors. Three different test datasets derived from the analysis of glass from known manufacturing origins (&gt; 400 samples from four (4) different plants) and using the ASTM analytical method for data collection, are interrogated using LR calculations. Three (3) different background databases are used to calculate the LRs. The first background dataset is derived from a collection of elemental data from ~ 500 different authentic vehicle glass samples collected over 2 decades. The second background was provided by the (BKA) forensic laboratory in Germany and includes ~ 430 casework samples from different sources and the third set originates from a law enforcement laboratory that has maintained elemental data for glass for more than 3 decades. The LRs calculated from comparing glass manufactured at three different plants over relatively short periods (over 2-6 weeks) result in a range of calibrated LR values from very low (LR~10-3) when the glass are manufactured at different plants or manufactured weeks-months apart in the same plant to very high (LR~103) when the glass samples either originate from the same source or were manufactured on the same day and in the same plant. Although some of the glass samples being compared may not originate from the same broken window source, they exhibit chemical similarity within these lower and upper bounds and the LRs presented here facilitate the correlation between chemical relatedness to manufacturing history, specifically the time interval between production. The overall aim of this research is to improve on the opinion statement provided to the court for the significance of finding matching glass evidence in a particular case.

Advancing reporting of significance from the analysis and comparison of glass evidence; A global collaboration

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.