Bridging the gap in forensic toolmark evidence using advanced correlation methods

"A tool used against a surface, for example in criminal activity, may leave an impression in the substrate material. Currently forensic investigation relies upon the visual comparison of 2D images of the impressions by expert examiners who base their conclusions on opinion. With the advancement of measurement technologies and comparison techniques, there is a gap between current capabilities in research and their use in criminal proceedings, which this project seeks to address. An interdisciplinary approach to areal measurement and correlation will be applied to toolmark investigation to achieve an objective, repeatable approach to the forensic comparison of toolmark evidence. When a tool comes into contact with a relatively softer substrate material, plastic deformation is caused whereby a permanent impression of the tool is imparted. Toolmarks are vital in within the forensic field for the determination of events at crime scenes, for example in instances of burglary or even when a tool leaves an impression in bone. While the comparison of toolmark evidence has been used in criminal proceedings for several decades, the methods that are accepted in court have not changed. This has resulted in methods being deemed as subjective and unrepeatable in scientific reports. While other evidence types have been able to apply modern measurement techniques, resulting in objective methods which are based on scientific standards, the same cannot currently be stated for impression evidence. Therefore, there is a gap between the methods available and those currently being used in forensic comparison.
The application of modern techniques will result in a change from 2D to areal measurement, and with this comes the acquisition of significantly more data with regards to topography of the toolmark. This ensures that the salient data has been captured, however with a larger amount of data comes the need to determine the correct processing methods for efficient correlation. Therefore, this research will focus on the application of processing methods to achieve a computational comparison, which has not been achieved yet. An interdisciplinary approach will be applied in which both scientific and engineering techniques will be utilised to acquire the knowledge currently needed in the field.
This project relies on a stepwise approach to build a method for the areal measurement and comparison of toolmark information. The first step will create a library of toolmarks in which variables in tool, operation and substrate material have been considered. This will allow forensically relevant controlled testing of the creation of the toolmark. Using advanced measurement techniques such as focus variation, interferometric techniques and profilometry, topography of the toolmark will be acquired. Computational processing will then be applied to separate the salient information for correlation, resulting in a method that can bridge the gap between current methods and the court room. "