Could it be because there is nowhere to bring one? If we assume most judges at this time are corrupt or corruptible (under threat to his family), then it is fruitless to bring a major indictment, much less, many indictments. So does this make Durham a failure? Not in my book, it makes him a cool and patient cookie.
Once the Military takes over Durham cashes in his pink slip to retirement and as he does so gives all his research to a military tribunal. Cool plan, eh?