Grand juries sit for months at a time, and a prosecutor has to bring cases before the grand jury before going to court. The grand jury decides if there is sufficient evidence for the case to go to trial. It's largely a formality. Essentially, the grand jury is there to answer the question of 'if these alleged facts are true, would that mean a crime has taken place?' Technically, the GJ's job is to find whether there is probable cause to issue an indictment and put someone on trial.

That's why you don't have a regular defense team there; the GJ isn't pronouncing on the guilt or innocence of the accused person, they're pronouncing on the gravity of the alleged offense. So if you're a prosecutor and you bring someone in front of a grand jury for murder, all you have to establish on a practical level is that a murder took place. You can learn more from the handbook for jurors: http://www.uscourts.gov/Viewer.aspx?doc=/uscourts/FederalCou...

There's no precrime involved here. A crime (vandalism of a federal court building) occurred in May, and it was brought before the grand jury that happened to be impanelled at that time, as one of the many cases they examine. It's not a conspiracy just because you don't know about it.