I always figured this was the case for a lot of common things like full-disk encryption schemes, AES, root certs, etc. If there's a break, they wouldn't use it in court unless it's taking down a very, very big target.
Why do we tolerate government corruption at the highest levels of law enforcement?
Sure. But then first you have to prove it is a parallel construction.
The purpose of laws like the 4A is to prevent the police from harassing innocent people by going on fishing expeditions. The purpose of the poisoned tree doctrine is to prevent the police from committing crimes as part of their work.
But if a plains-clothes police officer sees you load a kilo of cocaine into your car every Tuesday, on the same street corner, there's nothing illegal or immoral about him telling a uniformed cop to show up next Tuesday, to observe you doing just that. I see no reason why the uniformed cop should be compelled to reveal his source.
Now, if the plains-clothes officer was doing warrant-less break and entry in order to observe you doing the crime, that would be an ethical problem.
This does create a bit of a connundrum - where you often can't tell if parallel construction was used to cover for legal, or for illegal behaviour. But I see no reason for why the first case I presented should be forbidden. If pressed on the stand as to why the officer chose that street corner to be on Tuesday, they can avoid prejury by declining to answer, or just say that they were tipped off. I find it doubtful that a judge would compel the officer to answer, or to elaborate - he's not the one that's on trial, after all.
It all hinges on whether or not they had a warrant to surveill the ISIS site.
If the police have a warrant to plant a hidden camera at a crackhouse, I don't see why they would have to reveal its existence, when they later stop and search a car full of drugs at a perfectly legal search at a border checkpoint. If they didn't have a warrant... That's an ethical problem, and it runs afoul of the fruit of the poisoned tree.
Likewise, if there's an informant or a mole at the crackhouse, do you think the police are obliged to notify the world of his identity, every time they arrest someone he tips them off to?
If the defense asks at trial, what legitimate reason is there not to answer?
It's not exculpatory evidence, there is no obligation for the prosecution to turn it over. There's no reason for the judge to allow a line of questioning into it unless the defendant can make an argument as to why its relevant.
In reality I know that its difficult and unlikely to be proven or prosecuted, but it seems like that would be perjury.
Honest question though and I'm curious if someone with more expertise can explain where I'm wrong.