Books can be attributed to "Unknown" when the author or editor (as applicable) is not known and cannot be discovered. If at all possible, list at least one actual author or editor for a book instead of using "Unknown".
Books whose authorship is purposefully withheld should be attributed instead to Anonymous.
The final book of the law, mostly written by Moses (possibly finished by Joshua or a later writer). It ends with a very sad song by Moses telling Israel that they will inevitably forget God, follow idols, and be given up to their enemies until they return to God, which is exactly what happened.