This episode of the Just Science series of podcasts is the audio of an interview with Robert Thompson, a Senior Forensic Science Research Manager at the National Institute for Standards and Technology, who discusses his research on consecutively manufactured barrels and his recent research on "Objective Comparison of Striated Toolmarks Produced from Ten Consecutively Manufactured Cold Chisels Measured by Contact and Optical Surface Profilometry and Comparison Microscopy."
The focus of the interview is on techniques for determining whether a suspect chisel is the particular tool that made a suspected toolmark at a crime scene, thus suggesting that the suspect person in possession of the tool was using it at the crime scene at some point in time. Not only must the forensic scientist determine whether the suspect chisel is capable of making the crime-scene mark, but if so, was the suspect chisel the particular tool that made the crime-scene mark out of all chisels made in a consecutive manufacturing process. The research discussed in the interview involved using 10 consecutively manufactured cold chisels to determine whether particular chisels made distinctive marks in the same material (highly polished copper), such that it was possible to identify the chisel among the 10 that made the mark. The toolmarks were profiled using contact and optical surface profilometry and comparison microscopy. The toolmark profiles made by the 10 chisels were then compared for similarity and differences using two mathematical methods, cross-correlation function and the recently developed congruent matching profile segments method.