Abstract
There has recently been an increase in the research and implementation of advanced measurement techniques to ballistic toolmark identification. This has led to a shift from greyscale imaging to the acquisition of dense areal datasets. With the addition of mathematical correlation algorithms, these advanced techniques will be advantageous in criminal investigation. However, with the use of areal topography comes the addition of height point data which may differ in primer caps of varying material composition.This study discusses the differences in the overall topography of firing pin impressions in different primer cap materials, and the effect it has on the successful correlation of ballistic toolmark evidence.
Highlights
Current trends have seen an increase in research based around advanced measurement and correlation techniques in the comparison of ballistic toolmarks
Where grey scale image comparison relies on pattern comparison by eye which is related to the shadow and reflection marks on a surface, areal topography and mathematical correlation takes into account absolute height variations between the two surfaces [5]
Where there is a significant difference in brass composition it can be assumed that there will be a significant difference in material hardness, i.e. the more zinc the harder the material and topography of toolmarks imparted will be dissimilar
Summary
Current trends have seen an increase in research based around advanced measurement and correlation techniques in the comparison of ballistic toolmarks. The implementation of automated systems is expected to decrease the expense of correlation through automated elimination of definite non-matching toolmarks. This will leave a much smaller database of possible matching toolmarks for the expert examiner to compare, decreasing the correlation time and expense of correlation [1, 2, 3, 4]. To be able to implement advances techniques into ballistic toolmark investigation it is vital to understand the minute differences in toolmarks caused by the intrinsic variations described above. A softer material used for a primer cap would potentially contain a deeper and wider firing pin impression due to the increased materials flow resulting from a higher material ductility, with the opposite effect for harder primer cap materials
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