Evidential Value of Particle Combination Profiles On Common Items of Physical Evidence

As submitted by the proposer: This project will determine the evidential value of combinations of very small particles (VSP) as they occur on common items of physical evidence. VSP show exceptional promise to expand the numbers of cases where trace evidence can be used and provide quantitative statistical measures of evidential value. The laboratory analyses are highly efficient and can be conducted using existing crime laboratory personnel and equipment. Methods of particle combination analysis, developed and tested as part of prior NIJ-funded research, allow quantitative statistical measurement of correspondence and evidential value. They simultaneously exploit large numbers of very small particle types, with practical analysis times and levels of effort. The next step is to measure the evidential value of VSP on commonly encountered, important items of physical evidence. This project will use established analytical tools and statistical methods to determine the evidential value of VSP profiles found on handguns, cell phones, drug packaging, and ski masks. Project objectives are to: (1) expand, refine and test VSP harvesting protocols to accommodate non-porous, paper, and fabric surfaces; (2) harvest VSP from 100 evidence items (25 of each type); (3) apply the established analytical and interpretive methods to measure evidential value, and (4) present the project results to the forensic practitioner and research communities in an interactive format allowing full presentation and thorough discussion. Using protocols designed and tested under this project, duplicate samples of VSP will be harvested from 100 evidence items from the San Diego County Sheriff’s Office. The samples of harvested VSP, each comprised of many hundreds to thousands of individual particles, will be prepared for efficient characterization. Analyses will be conducted at the Defense Forensic Science Center (an operational forensic science laboratory) employing semi-automated scanning electron microscopy with elemental characterization by energy dispersive x-ray analysis (SEM/EDS). Statistical methods of particle combination analysis will be applied to filter extraneous particles, define a set of highly discriminating target particle types, measure the strength of correspondence between profiles, and provide measures of evidential value under defined experimental conditions. The results will be (1) measures of evidential value of particle combination profiles on common evidence types, (2) improved understanding of how well particle combination analysis of VSP works in different situations, (3) enabling of specific follow-on research and prototype casework applications, and (4) furthering the development of solutions for important investigative problems that are unmet by current forensic laboratory methods. This project contains a research and/or development component, as defined in applicable law. ca/ncf