By Amy Feldman

By Amy E. Feldman

PHILADELPHIA (CBS) –New York Justice Sol Wachtler once said that grand juries were so likely to file criminal indictments, he could get a grand jury to indict a ham sandwich. And yet, in several high profile cases including those in Ferguson, and Staten Island, grand juries did not indict police officers who shot people. So what is a grand jury anyway, and why do they have power to decide who gets arrested?

A grand jury is a group of people who, like regular jurors, get called and sit for jury duty. But unlike regular jurors who hear cases where people have been charged with a crime, a grand jury is there to decide if charges should be brought in the first place. And that is – or should be – a low standard.

They don’t have to decide if someone is guilty. Only if there’s probable cause to believe he might have committed a crime.

And, while it’s usually the police who decide whether to arrest someone, in cases where the person who may be arrested is a police officer, it’s the practice to send those cases to a grand jury so the police aren’t filing – or failing to file – a charge against one of their own.

That’s why they leave that up to the grand jury to decide, whose decision may or may not seem kosher to outside observers.