If the investigators had legal authority to conduct such operations is one thing. However, they were acting as private citizens. This means that they taped themselves committing a federal felony, with intention. They should be prosecuted as such. Bloomberg has also taken a strong stand against what he refers to as "vigilantism" in New York City. However, his operatives are practicing just that, as he defines it.
I am also aware that the operatives acted as a "couple" during the entire episode, so there must have been some communication involved between them. Somehow, I find it hard to believe that the second person could just suddenly appear and fill out the paperwork, yet not arouse suspicion. As is usual, an attornies description of an action is normally quite different than that of the participants.
It would also be difficult for the operatives to have purchased handguns without false documents in other states, another felonious violation on the form 4473.:barf: