If I knew the agent and had a working relationship with him, I might let him know whether or not getting a subpoena would be worth his time.
He's trying to tie together a ring of fraudulent activity and something has led him to this account. More than likely, a subpoena would be worth his time.
Going back to 2009, I'd want to know a lot more about what "fraudulent activity" he was looking for. That is too broad, and if your FI didn't file a police report or SAR, then it didn't hit your radar. That's an open-ended question.
If I were calling an FI to ask for information or even just a "yes or no", I'd begin the conversation with as much information as I could divulge.
Also, without a working relationship with this agent, how do you know that he truly is an agent?
Sorry for the rambling sidestep of your question...