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Forensic Analysis Weighing Bullet Lead Evidence
Adding data on the correlation of older neutron activation analysis and more recent ICP-OES results and any additional data that address the accuracy or precision of the method.
Writing and documenting the unwritten standard practice for the order of sample analysis.
Modifying and validating the digestion procedure to assure that all of the alloying elements and impurities in all samples (soft lead and hard lead) are dissolved without loss.
Using a more formal control-chart system to track trends in the procedure’s variability.
Defining a mechanism for validation and documentation of future changes.
Recommendation: Because an important source of measurement variation in quality-assurance environments may be the analyst who makes the actual measurements, measurement repeatability (consistency of measurements made by the same analyst) and reproducibility (consistency of measurements made by different analysts) need to be quantified through Gage R & R studies. Such studies should be conducted for Federal Bureau of Investigation (FBI) comparison procedures.
Recommendation: The FBI’s documented analytical protocol should be applied to all samples and should be followed by all examiners for every case.
Recommendation: A formal and documented comprehensive proficiency test of each examiner needs to be developed by the FBI. This proficiency testing should ensure the ability of the analyst to distinguish bullet fragments that are compositionally indistinguishable from fragments with similar but analytically distinguishable composition. Testing could be internal or external (for example, conducted by the National Institute of Standards and Technology), and test results should be maintained and provided as appropriate. Proficiency should be tested regularly.
Recommendation: The FBI should publish the details of its CABL procedure and the research and data that support it in a peer-reviewed journal or at a minimum make its analytical protocol available through some other public venue.
Recommendation: The conclusions in laboratory reports should be expanded to include the limitations of compositional analysis of bullet lead evidence. In particular, a further explanatory comment should accompany the laboratory conclusions to readily portray the limitations of the evidence. Moreover, a section of the laboratory report translating the technical conclusions into language that a jury could understand would greatly facilitate the proper use of this evidence in the criminal