I agree with BigAl, your aerial surveillance for the city council is outside the scope of the FAA Special Rule for Model Aircraft (Section 336) - Fly for hobby or recreation ONLY. I think this is operating under FAA Part 107 and, at a minimum, requires an FAA Remote Pilot Certificate to be legal. In addition, when I fly under Section 336, my homeowner's insurance covers me for liability but for flights under Part 107, it doesn't. I need a separate liability insurance (like Verifly) to be covered for any Part 107 operations.
I'm not a legal expert so I don't know whether any evidence you may have collected without a Part 107 license would be deemed invalid.
I am a pilot and thus, thought of something else you might consider. NASA has an Aviation Safety Reporting System (ASRS), generally referred to as a NASA report. If a pilot unintentionally violates an FAA rule and voluntarily reports it using a NASA report, in general, it can immunize that pilot from any FAA legal enforcement actions. It's a great program, however, immunity is not assured if your violations were deliberate or if you file a NASA report after the FAA formally contacts you about an incident.
Since the FBI is now involved, you might file a NASA report ASAP to explain the scope of your aerial surveillance operations and then never do it again without a Part 107 license. I've never considered using a NASA report for drone operations but in your case, it might offer some extra protection against enforcement actions should the FBI decide to refer anything to the FAA.
Good luck and please let us know what happens.