Different users apply computer forensic systems, models, and terminology in very different ways. They often make incompatible assumptions and reach different conclusions about the validity and accuracy of the methods they use to log, audit, and present forensic data. In fact, it can be hard to say who, if anyone is right. We present several forensic systems and discuss situations in which they produce valid and accurate conclusions and also situations in which their accuracy is suspect. We also present forensic models and discuss areas in which they are useful and areas in which they could be augmented. Finally, we present some recommendations about how computer scientists, forensic practitioners, lawyers, and judges could build more complete models of forensics that take into account appropriate legal details and lead to scientifically valid forensic analysis. Categories and Subject Descriptors D.4.5 [Reliability]: Verification; D.4.6 [Operating Systems]: Security and Protection...