Go for the big cheese not the little guys, remember he gets his orders from above!
You squeeze the “stuff” out of the little guys so that they decide to save their own hides and provide evidence to skewer those above.
Anyone (BATF&E) that had knowledge of Fast & Furious, committed a crime.
Remember, Mr. Big always leaves his traces in the lower ranks ~ not with all of them, but with some of them.
I'd be bringing in his "peeps", and I think Issa's staff people know who they are by now.