I know their identity is secret, but hasn't anyone seen them walking in and out of the courthouse so as to state, in general, male or female, white or African-American. Or did they sneak them in and out through a backdoor?
I would not be surprised if they do have a private entrance. The media and people in the local legal profession probably do know who at least some of them are, but it may be a criminal offense to reveal their names.
Grand jurors are prohibited from speaking about the cases they review or what is said, who appears, everything. The proceedings are usually recorded, but the recordings can only be released by court order and usually in connection with a judicial proceeding in which the content of the proceedings is extremely relevant to an important legal issue.