Is a grand jury required to indict or is some prosecutor just covering his behind?
Not only is a grand jury required, it must be a federal grand jury, since the crime is a Federal one.
I tried a quick search to identify the current members for the Chatanooga district, but no luck so far.
I do not believe that the members can be "secret."
No, a grand jury is not required to rubber-stamp a prosecutor's view. They would be totally pointless if that were the case. That said, the standard for indictment is pretty low if I remember correctly.
You may have been asking if it necessary for a grand jury to meet and agree before any indictment is handed down. I don't believe so. I think a prosecutor who feels he has a strong case can indict without one, but I'm not sure.
Freepmail me if you'd like an example of a grand jury which did not indict on recommended charges.