Crystal clear connections - database matching unknown glass fragments to reference glass from ATM explosions

This paper introduces the concept of an operational reference glass database, specifically designed for broken glass fragments from ATM attacks, jewelry store robberies, and ramraids on high-end clothing stores. The database, initiated in 2014, is used to compare glass traces from organized crews involved said criminal activities. Utilizing LA-ICPMS, this study establishes a methodology for collecting reference glass samples from the scenes of the aforementioned crimes, thus creating a comprehensive database containing over 3500 reference glass samples from crime scenes. The operational database is employed to match trace elemental profiles of glass fragments from suspected items to known reference samples, offering specificity and accuracy. Analysis of results, while ongoing due to the nature of active cases, find matches of trace materials in over 50 % of case requests since 2019. Challenges such as database scalability and continuous updating are acknowledged, and future directions include technological advancements to enhance precision and the application into other areas of forensic material analysis. The paper emphasizes the efficacy of this specialized approach in chemical profiling, providing a potent tool for linking glass traces to specific criminal contexts and providing intelligence and investigative leads into individuals involved in ATM-related crimes.

A multivariate extension to the standard 4σ criterion for comparison of forensic glass evidence

This manuscript presents a more accurate and easy to implement multivariate generalisation of the international standard 4σ forensic glass comparison technique. Many crimes result in glass breaking, and the broken glass found at a crime scene can be important forensic evidence. The chemical composition of this glass can be measured to establish whether it can be distinguished from glass fragments found on a suspect's clothing. The chemical composition can be measured using laser ablation-inductively coupled plasma mass spectrometry. A commonly used method to compare fragments of glass is the 4σ interval criterion. This method, however, compares each element individually and does not take advantage of the multivariate nature of this data. We introduce a multivariate extension to this method, which makes use of the correlation structure between the elements. We demonstrate that this method results in an improvement in the false positive rate, with only a small compromise in the false negative rate. The improvement in false positive rate is desirable as false positives translate to misleading evidence against a potentially innocent defendant. The multivariate generalisation improves accuracy while retaining a similar interpretation, and so is suitable to present in court.

An interlaboratory study evaluating the interpretation of forensic glass evidence using refractive index measurements and elemental composition

Seventeen laboratories participated in three interlaboratory exercises to assess the performance of refractive index, micro X-ray Fluorescence Spectroscopy (μXRF), and Laser Induced Breakdown Spectroscopy (LIBS) data for the forensic comparison of glass samples. Glass fragments from automotive windshields were distributed to the participating labs as blind samples and participants were asked to compare the glass samples (known vs. questioned) and report their findings as they would in casework. For samples that originated from the same source, the overall correct association rate was greater than 92% for each of the three techniques (refractive index, μXRF, and LIBS). For samples that originated from different vehicles, an overall correct exclusion rate of 82%, 96%, and 87% was observed for refractive index, μXRF, and LIBS, respectively. Special attention was given to the reporting language used by practitioners as well as the use of verbal scales and/or databases to assign a significance to the evidence. Wide variations in the reported conclusions exist between different laboratories, demonstrating a need for the standardization of the reporting language used by practitioners. Moreover, few labs used a verbal scale and/or a database to provide a weight to the evidence. It is recommended that forensic practitioners strive to incorporate the use of a verbal scale and/or a background database, if available, to provide a measure of significance to glass forensic evidence (i.e., the strength of an association or exclusion).