Special counsel Robert Mueller is likely to wrap up his investigation soon and issue a confidential report to the attorney general. It is important to understand the legal status of such a report and how it should be released and evaluated under the Justice Department regulations governing special counsels.

First and foremost, because it is the report of a prosecutor, it will inevitably be one-sided. Prosecutors pick the witnesses they present to a grand jury. Defense lawyers are not allowed to appear with their clients, or...