If the identity of the accuser(s) is being concealed from an accused, the investigation is simply fishing for an easy confession, because if a confession can be obtained, the burden of proof is lifted, rendering an accuser, eyewitnesses and additional evidence to be no longer necessary.
Secularly and scripturally, the accused (if he/she has not confessed) holds the right to know/face the accuser. (Matthew ch18) <edit
If that right to know/face the accuser is denied... then immediately deny the accusation. The case should then go cold and be held abeyance or entirely dismissed.
However, by WT policy, even an innocent person can be viewed negatively because "he should also have a fine testimony from outsiders" 1 Tim 3:7
In some cases, the only path to true exoneration would be to bring a successful countercharge of slander; but in WT world, that option often presents new risks which may not be worth the hassle.