AFTE Store - 2D and 3D Topography Comparisons of Toolmarks Produced from Consecutively Manufactured Chisels and Punches

A 2009 report by the National Academies recommended strengthening the scientific basis of procedures and criteria employed by the forensic science specialty of toolmark identification. The current method of comparison and determination of identity is conducted by a trained examiner using a comparison microscope. However, the ultimate conclusion of the comparison is subjective in nature and is affected by the examiner’s skill and experience. This study seeks to evaluate whether a mathematically objective metric, the maximum value of the normalized Cross Correlation Function (CCFmax), can be employed to identify the tool that generated a striated or impressed toolmark from a pool of consecutively manufactured tools. The metric will be applied to the measured surface topography of toolmarks generated under laboratory conditions on a near pristine surface. A device was designed for the controlled generation of toolmarks. Two types of representative tools were selected: chisels for making striated toolmarks and drift punches for making impressed toolmarks. For striated toolmarks, a 2D stylus instrument was used to capture the toolmark topography. Impressed toolmark topographies were captured using a 3D disc scanning confocal microscope. The comparisons were blind, with fully automated data analysis and identification. Based on the CCFmax metric and a statistical analysis of the known match and known non-match scores, all the unknown toolmarks were correctly identified to the tool that created them. This study provides additional objective scientific support for the validity of toolmark identifications.

Full Journal: AFTE Journal Vol 46 No 2 (2014)