The large amounts of data that have to be processed and analyzed by forensic investigators is a growing challenge. Using hashsets of known files to identify and filter irrelevant files in forensic investigations is not as effective as it could be, especially in non-English speaking countries. This paper describes the application of data mining techniques to identify irrelevant files from a sample of computers from a country or geographical region. The hashsets corresponding to these files are augmented with an optimized subset of effective hash values chosen from a conventional hash database. Experiments using real evidence demonstrate that the resulting augmented hashset yields 30.69% better filtering results than a conventional hashset although it has approximately half as many (51.83%) hash values.