I think, read the same book once, but this book was about a british wizarding school, where a few teachers and students used black magic, which ain´t comparable to our situation, I guess. Yes, id would be a very good explanation, how the scum could survive, if they have men, which are government emloyees and I really think, that at least one or two policemen/women are corrupt too.
If we sit back the Mafia would win some time, but if we kill randomly people because of small lines or studdering we will presumably help them to get us killed.
Still noone was killed, I think, we should wait till the first body is laying around, then we should look for ecvidence.
We won´t find any hint before a crime is done.