Software used for digital forensic investigations requires to be verified against reliability and validity criteria. In this paper, three well known tools are tested against the mandatory features of digital forensic tools published by the National Institute of Standards (NIST). It was found that a variation in performance existed between the tools, with all having measureable areas of non performance. The findings have an impact on the professional use of the tools and illustrate the need for benchmarking and testing of the tools before use.