Comey is moving towards declaring indictments. Grand Juries are there. Impeachment.

[Volaris]

35. A grand jury

Is a court operation in which evidence is put before the court to determine if that evidence will support charging someone(s) with a crime. If yes, charges are filed.
If no, everybody goes home. Because of the possibility of either being the case, grand juries and the evidence they consider are usually sealed until a decision is made.

Grand Juries don't file charges of their own volition, they just make recommendations to charge with crimes or not.

But if someone (either State AG or feds) put that information to a court TO MAKE SURE they're not wrong in what they're seeing or how to proceed if they are wrong (go get evidence of X, because this ain't enough) it means someone wants their shit together so that WHEN charges get filed, that's an airtight case and NOBODY goes home.

I'm not a lawyer.