Are you thinking of this instance? It's an instance that could happen to any of us. The CSAM in question was found (and only found) in garbage data in unused storage. And it means our GS tech had actively scan (go out of his way), rather than just fix the machine.
It also means it's inconclusive, since that kind of stuff can end up in your webcache through malware vectored through advertising. CSAM is weaponized in malware. Heck, there are CSAM images in the Bitcoin blockchain file (or were, if they found a way to scour them). Not that innocent websurfers have not been falsely convicted due to invisible crap in their cleared webcache, but we should know better by now.
It does raise a question about what you believe regarding the limits of our civil rights. Do you believe evidence illegally obtained by law enforcement should be wholly admissible if the crime is heinous enough? SCOTUS does, and ruled that even drug possession discovered during an illegal search should be admissible. But that pretty much means you and I cannot rely on constitutional protections from unreasonable search and seizure.
Here in the States, preserving our protections and our privacy sometimes means defending the worst people. See, it's supposed to be a penalty against the state for poorly executing the law when someone can't be convicted due to inadmissible evidence. If a guilty citizen is improperly treated by law enforcement (according to the legal theory that supposed Blackstone's ratio) then they should be acquitted, and the public has only the incompetence of state actors to blame.
Law enforcement is supposed to respect your protections, and if we let them conduct illegal searches (such as buying data from brokers, or using IMSI spoofers without a warrant, or asking Google for everyone within a mile and an hour of a criminal incident) then they're going conduct those same illegal searches when you're working with your mutual aid organization or are protesting against injustice. If serial killers and child molesters aren't protected from overpolicing, then you aren't either, and if you happen to be nonwhite, LGBT+ or part of another marginalized group (Juggalos!) then you're in far more danger of illegal searches, false convictions and prison time, assuming you're just not the victim of an officer-involved homicide.
If you live in the US, it's very difficult not to commit crimes, particularly federal felonies. There but for your privacy (and / or the grace of prosecutorial discretion) goes your freedom and reputation.
That said, the FBI has been super sloppy in its pursuit to hunt down CSAM traders, even letting their high-end malware leak into the public to be dissected and used by black-hats, and interests of rival nations.