It is SOP for the Feds to start at the bottom of the chain and work up.  This is to persuade those
on the lower rungs to   testimony against the bigger fish in exchange for leniency.
This particular Federal Grand Jury is going to end shortly but will be replaced by another
which will probably be the one to indict the bigger fish in the chain. 
Here in our Republica Bananera, our ruling political elite and others who are connected to them
have little fear of being investigated or prosecuted on the City or State level as the place is run
like an organized crime family.  Not so with the Feds which is why most if not all of the notable prosecutions of corrupt politicians and their cronies here have occurred on the Federal level.
The most recent one that comes to mind is Albert Hee, brother of former state senator Clayton
Hee.