When you "observe this account and search for anything we can use to get a subpoena", have you not made yourself an agent of the government? You are now looking

When you "observe this account and search for anything we can use to get a subpoena", have you not made yourself an agent of the government? You are now looking at client information on request of the government. I'd think that triggers the "unreasonable search and seizure" and could (I hope) result in a mistrial.