He wanted to sue the government for its obvious manipulation of a grand jury to create a crime that wasn't there. Attorneys warned him that it would probably be fruitless. So far, they've been right. But it has made it nearly impossible to punish them when they abuse that right. The grand jury process today is as far afield from what it was intended to be as it could possibly be.
Federal prosecutors have tremendous power when they convene a grand jury.
They decide whom to seek indictments against and what charge that suspect should face. They also determine what evidence grand jurors see, what witnesses they hear and whether to grant leniency to witnesses who might testify against a defendant. They can frame arguments that favor their version of events, emphasize the testimony of one witness, and ignore the testimony of another. Evidence presented before a grand jury may be so flimsy that it would not be admissable at a trial. Grand jurors may hear rumors from witnesses or even use their own knowlege of an alleged crime in determining whether to indict.