The Chofetz Chaim had mentioned in his note that you must first tell the victim what had happened to him and who did it before you tell anyone else in matters where it’s unlikely or not the situation where he would be compensated. This is because word spreads and if he finds out second hand what happened that might make matters worse and create a tremendous fight. We want to avoid internal fight amongst the Jews. The #1 reason for arguments is rechilus, people tell on each other to others in a fashion which allows a bad situation to escalate. Hashem created a prohibition of rechilus (which the Chofetz Chaim discusses in the next part of this book, after chapter 10) just for this reason, to minimize the possibility of finding amongst His children. A person might make an excuse for himself that he would be allowed to tell others, before he tells the victim, assuming he meets all the rules, because anyways there is a chance, albeit a farfetched chance that maybe the criminal will repent and give back what he owes. But we have to assume that it is a farfetched chance that he will actually repent since he was already rebuked and didn’t listen or is known not to listen to rebuke, therefore, unless it is probable compensation can be exacted then it is forbidden to spread the word if what happened before telling the victim even if it is for the proper intent of teaching people not to follow the ways of this evildoer. It is better to not cause fighting amongst the Jews then teach others a lesson not to follow in the bad ways of these criminals.
Furthermore, you have to be careful who you give this information to, for if you tell people who aren’t willing to listen to your warnings not to follow the ways of the criminal, for example if you are talking to people who are also thieves or part of the mafia who don’t care about the way this criminal acted. Then you might cause them to speak rechilus because they might tell the criminal what you told them, even if you met all the rules and had the right intent to try to stop them from following what he did, but telling the wrong people might escalate a big argument and might even cause them to tell on you to the government or other non-Jews and create serious problems for the Jews.
It also doesn’t matter if someone asked you what happened or you just tell them if you are allowed to then it’s fine if not, then not. Many times people make up excuses that they can tell their family members what other people have done to them, and it’s a mitzvah to do so because the verse in Yeshayahu 58:7 says “You shall not hide anything from your own flesh and blood” However only if all the prerequisites are met them you can tell them if not, then it’s absolutely forbidden and straight out rechilus/lashon hara.