First, there is the historic fact that grand juries were made up of laypersons. When the Puritans arrived on the Mayflower in 1620, they brought with them their culture, which included the law of England. That consisted of the common law -- that is, the judge-made law built up over centuries -- and all legislation enacted by British Parliament. Since there were no cops (until 1820), folks had to enforce the law.
The American colonists empaneled men for a two-year hitch as Grand Jurors. These men could look around for crime, and for physical trouble such as a bridge in need of repair.
Note: I’m sure those colonial grand jurors felt duty-bound to help society. And so they should! Today, when a prosecutor or judge sits in the Grand Jury room, this waters down the felt responsibility of citizens.
Second, there is a clear statement about our right to set up a grand jury, by US Supreme Court Justice Scalia in the 1992 case US v Williams (albeit written in dissent and thus not binding.) I quote:
"... citizens have the unbridled right to empanel their own grand juries and present 'True Bills' of indictment to a court, which is then required to commence a criminal proceeding. Our Founding Fathers presciently thereby created a 'buffer' the people may rely upon for justice, when public officials, including judges, criminally violate the law….”
