What is a Grand Jury...

Everybody's talking about it but on one has explained what it is or how it works.
I knew the basics just like everybody else... oh well, at least I thought I did... but I also knew I certainy missed a few details.
Thankfully NPR has fixed this with a very illuminating article on how Grand Juries work.

To put it in a nutshell:

A grand jury does not determine guilt or innocence -- only whether there's probable cause to believe a person or persons committed a crime. A grand jury decides whether to bring charges via a written indictment.

Federal grand juries are composed of 16 to 23 individuals selected at random "from a fair cross section of the community" in the district in which the grand jury convenes, according to the Federal Grand Jury Handbook. The names are generally drawn from lists of registered voters. Twelve of the minimum 16 members required to be present must vote in favor of an indictment before it can be returned.