Suppose, for discussion, that the defense is short of time, money, or brains: in which case the agent-of-government may not even have come up.
So from the prosecution perspective: better not to mention it and hope it never comes up. This is how citizen rights are "innocently" violated wholesale, and it happens all the time.
Worse, it only came up because the Best Buy agent was paid. Suppose a different scenario: the Best Buy agent was cooperating to avoid prosecution for something they did. Well, that makes it all better, doesn't it, to have them directed by the FBI and no money changing hands--and also much harder for the defense to prove.
The problem is, first, the direction of a confidential agent by the FBI (whether paid, quid pro quo, or volunteer) and, second, the FBI's (repeatedly demonstrated) willingness to conceal the fact that the agent was under FBI direction.
The bottom line was that the FBI hoped it would remain unnoticed that such a relationship existed. As they see it, just bad luck that this time it got found out. Better luck next case.
IMSI catchers are getting so common it's getting to where you're more likely to connect to one of those than to a regular cell tower.
Maybe we're thinking about this backwards.
Maybe the proper approach is to simply order law enforcement (i.e. government) to operate the entire cell network. Yeah, no privacy, but that ship has apparently sailed already. Certainly Congress isn't going to help--three guesses what any IMSI catcher law is going to do for privacy: nothing, nothing and nothing.
But think of the benefits: Coverage would improve. No more roaming. No more "can you hear me now" shill commercials. No more data caps. Probably many more.
While we are sensitive to the Department’s need for discipline throughout the chain of command, the policy here and the disciplinary actions taken pursuant to it would, if upheld, lead to an utter lack of transparency in law enforcement operations that the First Amendment cannot countenance.
But-but-but that just can't be what Chief Despot Dixon intended!
I really like the party line buy-in that, "EVERY SAMSUNG NOTE 7 WILL EXPLODE IN FIFTEEN SECONDS...TICK...TICK...TICK...!!!"
Yes, Samsung had a problem. But it was "dozens of phones" out of 2.5 million. "Dozens" is a bit nebulous but, if it is still the correct term, then probably not over a gross (144). On that basis the chances of a Note 7 failing are 1-in-17360, about the same as that of your dying next year in an automobile accident.
Oooo...and there's 133,000 of those Note bombs still out there, "...ANOTHER EIGHT MIGHT EXPLODE!!!"