Assessing the Strength of Trace Evidence Fracture Fits Through a Comprehensive, Systematic, and Quantifiable Approach

Criminal activities such as sexual assaults, kidnappings, hit and runs, and homicides often lead to the fracturing of materials. The realignment between fragments left at the scene and those recovered from an individual, or object of interest, could become crucial evidence during the investigation. These fracture fits are often regarded as the highest degree of association of trace materials due to the common belief that fracture edges often produce individualizing patterns. Nonetheless, there is not enough proof of the scientific validity of this assumption. Currently, the examination of fracture edges involves subjective judgment of the examiner without quantifiable uncertainty. There are no consensus-based standard methodologies for the identification of distinctive features on a fractured edge, a systematic criterion for informing a match/non-match decision, or methods for assessing the weight of the evidence. Thus, there is a critical need to develop, validate, and standardize fracture fit examinations and their respective interpretation protocols. In the absence of such foundations, the assessment of the value of the evidence and the reliability of the expert’s testimony would remain challenging.

The overall goal of this proposal is to develop an effective and practical approach that provides an empirically demonstrable basis to assess the significance of trace evidence fracture fits. Our specific goals are first, to develop a systematic method for the comparison of fracture fits of common trace materials such as duct tapes, textiles, and plastics, using both human-based protocols and automated computational algorithms. Second, to develop a relevant extensive database of over 9,000 samples to assess the weight of a fracture fit using similarity metrics, probabilistic estimates, ROC curves, score likelihood ratios, and a two-stage interpretation method. Third, to evaluate the utility and reliability of the proposed approach through inter-laboratory studies that can establish consistency base rates. The strategic partnership of experienced forensic researchers, computational material science physicists, statisticians, and practitioners will be crucial for planning the adoption of the developed approaches within crime laboratories.

Our proposal specifically addresses the research needs identified by NIST-OSAC and the NIJ-TWG (quantitative assessment of error rates, scientific foundations, standardization, validation, interpretation, casework review, and proficiency assessment). As a result, this study is anticipated to transform current trace evidence practice by providing—for the first time—harmonized examination protocols and decision thresholds, effective mechanisms to ensure transparent and systematic peer-review process and interlaboratory testing, and quantitative basis that substantiate the evidential value of fracture match conclusions. Note: This project contains a research and/or development component, as defined in applicable law, and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14). CA/NCF