Wow - what a lot of effort to nail someone who the feds become suspicious might be flying without a current medical and possibly altering a tail number:
October 12, 2011: Initial report of suspicious activity by a helicopter owner.
October 17, 18, & 19, 2011: Agents discover initial reports unfounded. But they do discover the medical for the alleged pilot-owner is not current. Over the course of three days they find some tape on a tail number that appears to alter it. During surveillance they observe tape being removed before an actual flight. Story does not claim any flights to have occurred with altered tail number. Feds do observe a flight with 3 people where they think the non-medically current pilot-owner acted as pilot, but can't prove it since one other was also qualified to pilot. (Not sure if agents were aware that helicopters are generally piloted from the right seat.)
May 30, 2012 (6 months later! Why?) Feds get a grand jury indictment (and presumably an arrest warrant) against pilot-owner for false or misleading tail number and flying without a current medical. They do not immediately act on the warrant or indictment because they actually have no evidence to convict.
Based entirely on this chain of non-criminal events, agents begin surveillance of the airport (when they began surveillance is unclear - October or May?) in hopes of catching the pilot-owner piloting without a current medical.
July 30, 2012 (8 months later! Surveillance cost for this period is...?) The agents allegedly finally observe the pilot-owner flying the helicopter solo without a current medical. Agents direct ATC to lie to pilot so as to get him to return to airport, where he is arrested.
It isn't clear whether the feds ever saw the helicopter being flown with altered tail numbers or that that part of the indictment will be pursued by the prosecutor.
This is an incredible amount of labor and effort on the part of the feds with low chance of it all panning out. No wonder they wanted to seize the helicopter; they are unlikely to want to walk away empty handed for that amount of effort. Not sure why they pursued this.