It might take a happenstance like illegal money laundering offshore to open their eyes.
There could also be illegal converting and money laundering in casinos---where the perps sign up for high roller comp programs. That leaves a clear trail for the IRS since the casinos record every transaction.
What I want to know is how to investigate these guys and reveal them for what they are doing? I am not all that savy, but I am sure I could get some good advice from a few.