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

• NCJ Number: 309918
• Author(s): Tatiana Trejos; Aldo Romero
• Date Published: June 2024
• Length: 132 pages
• Grant Number(s): 2020-DQ-BX-0012
• Agencies: NIJ-Sponsored
• Publication Type: Research (Applied/Empirical)
• Award: Assessing the Strength of Trace Evidence Fracture Fits Through a Comprehensive, Systematic, and Quantifiable Approach

Annotation

This paper reports on a research project that aimed to develop an effective and practical approach that provides an empirically demonstrable basis to assess the significance of trace evidence fracture fits, addressing several research needs identified by NIST-OSAC and the NIJ-TWG, and, as a result, is expected to transform current trace evidence practice.

Abstract

The final report describes a research project with the following goals: to develop a systematic method for comparing fracture fits of common trace materials such as duct tapes, textiles, and automotive plastics, using both human-based protocols and automated computational algorithms; to develop a relevant extensive database of nearly 9,000 samples to evaluate performance rates in the field, and assess the weight of a fracture fit using similarity metrics, probabilistic estimates, and score likelihood ratios; and to evaluate the utility and reliability of the proposed approach through inter-laboratory studies that can establish consistency base rates. The report provides a detailed summary of the project, noting research design, methods, and data analysis, as well as outcomes, and results and findings. Some of the major findings are: that not every physical fit determination holds the same probative value; the fracture edge features that are relevant and more individualizing are particular to each material composition, construction, and separation method; there is a risk of introducing bias and errors when the examination of physical fits is constructed solely based on the judgment of the examiner; and overall performance rates evaluated in the project demonstrate that accuracy of physical fit examinations is high with a very low incidence of false positives.