I would still like to ask you about speaking loshon horah/rechilos about someone who was niftar if this person caused me harm and statements made by me about him would help me in a court of law.
Included in this question- does this person get punished in the next world when bad things are spoken about him?
Speaking lashon Hara on the deceased is as severe (if not worse) than speaking about a live person.
(מרדכי ב"ק, פרק החובל, בשולחן ערוך או"ח תר"ו, ג, שולחן ערוך חושן משפט סימן תכ, לח, חפץ חיים ח:ט)
However, in these sources though, there is no reference to what happens to the person if bad things are spoken about him, though the people who spoke the bad things must ask forgiveness .
In addition, in a case when some is already accused of a wrong doing he cannot remove the guilt from him by placing it on someone else by means of Lashon Hara. He is only allowed to say that he is not guilty. The Chaftez Chaim compares this to a situation that a person may save himself from a coming damage even if it may cause damage to another. However, in a case where the damage already came, in this case already accused, he may not place the blame on someone else.(חפץ חיים, הלכות לשון הרע כלל י, יז, מג, שולחן ערוך חושן משפט שפח:ב)
Now since it seems the case you are mentioning is real and has ramifications on actual people and not in theory, as I have already said in my previous answer, as much as I would like to help, sometimes the issues presented are complex and cannot always be handled over the internet. The Chaftez Chaim himself says that in an actual case, this issue of not being able to clear one's name from guilt, is not clear enough to him, so you can understand my position. Therefore, I suggest you turn to a prominent Dayan=Rabbinical judge to assist you in this issue.