PML study supports validity of toolmark identification in forensics
For the better part of a century, forensic examiners have relied on comparison microscopes to compare the microscopic features of toolmarks found at a crime scene with those generated by suspected tools. The process relies on an examiner's training, experience, and judgment to assess the whether two compared toolmarks are more similar than toolmarks generated by different tools. Furthermore, the microscopic images provide only an indirect measure of the underlying toolmark surface topography though slope variations and shadowing, and are affected by lighting conditions, exposure settings, and variations in reflectivity.
In 2009, the National Academies published the report "Strengthening Forensic Science in the United States: A Path Forward," which called into question the objectivity of conclusions based on visual toolmark identification by examiners. A major concern is the lack of precisely defined, and scientifically justified, protocols that yield objective determinations of a match or non-match with well-characterized confidence limits and/or error rates. PML researchers Xiaoyu (Alan) Zheng and Johannes Soons of the Semiconductor and Dimensional Metrology Division, and Summer Undergraduate Research Fellowship (SURF) students John Villanova (2012) and Taher Kakal (2013), have responded to this criticism by seeking to strengthen the scientific basis of the toolmark identification process through the use of mathematically objective similarity metrics applied to direct measurements of the surface topography. The work builds on research by the Surface and Nanostructure Metrology Group and the NIST Office for Law Enforcement Standards (OLES) on forensic firearm identification using toolmarks found on bullets and cartridge cases.
For this study, Zheng obtained 10 consecutively manufactured chisels (for making striated toolmarks) and 10 consecutively manufactured drift punches (for making impressed toolmarks) from a major commercial tool supplier.
- TAMS SEMICONDUCTOR LIMITED