A novel method for extracting forensic evidence from aluminum foil that has been used as part of a “foil impressioning” kit, using toolmarks comparison techniques

The "Foil Impressioning" kit is a common lockpicking tool for pin-tumbler locks. Using this kit includes assembling a shaped and grooved aluminum foil onto a blank key and inserting it into the keyhole. The lock can be opened by jiggling the tool both clockwise and counter-clockwise. At the end of the process, when the tool is removed, the foil may break off and get stuck in the keyhole. Although the suspect's DNA can be extracted from the foil, in several cases the suspects argued in court that someone else used a recycled aluminum foil that they had previously used for an innocent purpose, such as wrapping a sandwich. This study shows that there are differences in the manufacturing process of the foils that were purchased as "ready for use" ("pre-shaped and grooved foils") compared with foils that were "manually shaped and grooved" using the "manual tool" which is part of the kit. The suspects' arguments can be ruled out by forensically proving that the foils were purchased as "ready for use." The study also shows how toolmarks can be used to forensically link, by subclass characteristics, foils seized in the suspect's possession to those found at the crime scene. Thus, the evidence against the suspect is corroborated.