Quantitative Tools for Examination of Microscopic Fracture Surface Topology and Degradation for Physical Match Analysis of Evidence

As submitted by the proposer: This combined development and applied research proposal investigates the underlying scientific basis for the forensic analysis of fractured and torn surfaces, and environmental effects. The material intrinsic properties, the structure of its micro-constituents and the exposure history of external forces on a fragment of forensic evidence have the potential or Premise of Uniqueness to support our hypothesis in providing quantitative signatures of its microscopic surface features that can be used for forensic comparison, especially in absence of any direct one-to-one spatial relationship. The methodology utilizes machine-based 3D spectral analysis of the fracture surface topography, mapped by white light non-contact surface profilometers, (being developed under previous NIJ funding). The proposed analysis is self-calibrated for fracture-feature-characteristics of individual material class, allowing potential application across a broad range of fractured materials and/or toolmarks, with diverse textures and mechanical properties.
The proposed framework seeks to assist the examiner by providing analytical and statistical support for an examiner’s decision, which in some applications will be able to turn an inconclusive result into a conclusive match between a tip and a suspect tool or knife by providing an estimate (and confidence bounds) for the probability of a true match, given a quantitative match decision. In other situations, application of our proposed method will allow the examiner to exclude a tip from having been part of the suspect tool or knife, based on an estimate of the probability of an untrue/false positive match, given a quantitative not-match decision.
Two phases of work are proposed.
Yr-1: development of the mathematical and algorithm framework, and applied to controlled laboratory samples from pry tool steel and real parts, identifying key variables, probability distributions, and quantification of different sources of variability.
Yr-2: performance of a systematic study to different fracture scenarios and environmental conditions. We will examine the topology of fracture surfaces exposed to the degrading effects of controlled humidity and pH-level, in order to examine the applicability of the technique to weathered specimens. Testing protocols will be scrutinized by our forensic collaborator for deficiencies and suggest possible improvements. Successful advancement of the proposed technique has the potential to provide a new investigative machine-based analysis with quantified error probabilities that can be applied in performing physical matches for a variety of materials. This research will be conducted in response to the NIJ’s expressed need for knowledge underlying forensic science, and in collaboration with forensic scientists working in a forensic laboratory.

This project contains a research and/or development component, as defined in applicable law.

ca/ncf