The Analysis of Trace Forensic Evidence Using Isotope Ratio Mass Spectrometry: Differentiating Fibers

The majority of trace evidence cannot be conclusively linked to specific exemplars with a high degree of certainty. Chemical and physical properties of evidence can be shown to be consistent with exemplars, but often not linked to a specific exemplar. This limits the discriminatory power of trace forensic evidence for attributing crime scene evidence to a single suspect. Isotope ratio analysis, using isotope ratio mass spectrometry (IRMS), holds promise for changing the current level of discriminatory power available for the analysis of trace evidence. Forensic isotope ratio mass spectrometry, a relatively small field of forensic analysis, may well be able to provide discriminatory power to trace evidence similar to that available for drug analysis by GCMS or biological sample analysis using nuclear DNA typing. This would allow trace evidence to be linked to a single suspect or source with a high degree of certainty, increasing the probative value of trace evidence. More research is needed in order to develop more forensic applications of isotope ratio mass spectrometry and allow the technique to mature so that it can fulfill this promise. This proposal aims to apply isotope ratio mass spectrometry to the analysis of fibers. Fiber evidence may be important in a variety of cases, including kidnapping, murder and assault cases. Development of an isotope ratio mass spectrometry technique for fibers will not only provide higher levels of discriminatory analysis for these samples, it will also expand the number of forensic applications where isotope ratio mass spectrometry can be of significant value. The overall goal of the proposed research is the creation of useful methods for the differentiation of fibers based on isotope ratio mass spectrometry for criminal justice purposes. We propose to use isotope ratio mass spectrometry to determine the isotope ratios, namely ä2H, ä13C, ä15N, and ä18O, for fibers that are otherwise chemically and physically identical. Isotope ratio analysis has previously been shown to be able to differentiate different samples of illicit drugs, explosives, and plastic bags that are otherwise indistinguishable. These differences may result from differences in the geographical origin of the samples or from different manufacturing batches created at the same site but at different times. We will create isotopic composition plots using combinations of isotopes (i.e. ä2H and ä13C, ä13C and ä15N, ä2H and ä15N, etc.) as well as plots that compare three isotopic compositions in order to determine the isotopic compositions with the most discriminatory power for our samples. Statistical analysis will be used to determine similarities or differences between fibers. We expect to present the results of our research at two national scientific meetings as well as submit three manuscripts detailing the results of the various fiber analysis for peer-review and publication. We will also produce interim reports and a final report for the National Institute of Justice (NIJ) detailing our results. Data sets will be made available upon request for archival in the NIJs Data Resource Program. ca/ncf