Subpoena the underlings, offer them immunity to talk and implicate their bosses and take it as high up the food chain as you can (hopefully, Zero will be there in the net, too!).
That's the other side of silence. You can be silent all you want, but that doesn't stop the prosecution from getting other witnesses and having them tell the story, entirely unopposed by you because you are silent.
If the prosecutor goes low enough s/he will always find a worker bee who saw and heard something and who has neither a reason nor the right to remain silent. 5A only allows you to not be a witness against yourself. You cannot remain silent about someone else's crime; that may earn you a few conspiracy charges. I recall that in Clinton's days someone spent a good time in jail for refusing to speak about other people's deeds (that was contempt of the court.)