Tool mark identification relies on the premise that microscopic imperfections on a tool's working surface are sufficiently unique and faithfully transferred to enable a one-to-one association between a tool and the tool marks it creates. This paper presents a study undertaken to assess the validity of this premise. As part of this study sets of striated tool marks were created under different conditions and on different media. The topography of these tool marks was acquired and the degree of similarity between them was quantified using well-defined metrics. An analysis of the resulting matching and nonmatching similarity distributions shows nearly error-free identification under most conditions. These results provide substantial support for the validity of the premise of tool mark identification. Because the approach taken in this study relies on a quantifiable similarity metric, the results have greater repeatability and objectivity than those obtained using less precise measures of similarity.

Forensic analysis of glass samples was performed in different laboratories within the NITE-CRIME (Natural Isotopes and Trace Elements in Criminalistics and Environmental Forensics) European Network, using a variety of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) systems. The main objective of the interlaboratory tests was to cross-validate the different combinations of laser ablation systems with different ICP-MS instruments. A first study using widely available samples, such as the NIST SRM 610 and NIST SRM 612 reference glasses, led to deviations in the determined concentrations for trace elements amongst the laboratories up to 60%. Extensive discussion among the laboratories and the production of new glass reference standards (FGS 1 and FGS 2) established an improved analytical protocol, which was tested on a well-characterized float glass sample (FG 10-1 from the BKA Wiesbaden collection). Subsequently, interlaboratory tests produced improved results for nearly all elements with a deviation o

Ti) to use for discrimination among the glass samples. This multi-element discrimination showed a significant improvement in the discrimination statistics over using only refractive index (RI) measurements. Oak Ridge National Laboratory (ORNL) recently analyzed fragments from 76 of the original side window fragments using inductively coupled plasma mass spectrometry (ICP-MS). The ICP-MS analyses measured 45 elements using a hierarchical sampling scheme to estimate variances due to sampled population (V P ), variance due to sample dissolution and within sample heterogeneity (V D ), and variance due to replicate measurements (V M ). The between-to-within ratio [B/W ~VP /(V D 1 V M )] afforded a measure of the variance within the population to that in the analytical measurement, providing a first approximation of the discriminating power of each element. Florida International University updated the RI measurements on 72 available glass fragments. These RI measurements along with ICP-AES and ICP-MS elemental analyses were used for pairwise comparisons of all possible pairs of the 72 glasses that had a complete set of measurements. The pairwise comparisons used Tukey's HSD method to compare RI and element-by-element discrimination potential of ICP-AES and ICP-MS for analyzing glass in forensic casework.

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Elemental analysis of glass was conducted by 16 forensic science laboratories, providing a direct comparison between three analytical methods [micro-x-ray fluorescence spectroscopy (μ-XRF), solution analysis using inductively coupled plasma mass spectrometry (ICP-MS), and laser ablation inductively coupled plasma mass spectrometry]. Interlaboratory studies using glass standard reference materials and other glass samples were designed to (a) evaluate the analytical performance between different laboratories using the same method, (b) evaluate the analytical performance of the different methods, (c) evaluate the capabilities of the methods to correctly associate glass that originated from the same source and to correctly discriminate glass samples that do not share the same source, and (d) standardize the methods of analysis and interpretation of results. Reference materials NIST 612, NIST 1831, FGS 1, and FGS 2 were employed to cross-validate these sensitive techniques and to optimize and standardize the analytical protocols. The resulting figures of merit for the ICP-MS methods include repeatability better than 5% RSD, reproducibility between laboratories better than 10% RSD, bias better than 10%, and limits of detection between 0.03 and 9 μg g(-1) for the majority of the elements monitored. The figures of merit for the μ-XRF methods include repeatability better than 11% RSD, reproducibility between laboratories after normalization of the data better than 16% RSD, and limits of detection between 5.8 and 7,400 μg g(-1). The results from this study also compare the analytical performance of different forensic science laboratories conducting elemental analysis of glass evidence fragments using the three analytical methods.