Epstein was reportedly suicidal weeks before his death. I remember he also had a few visits from his lawyer prior to killing himself.
At the time none of us cared that it was epstein was the one who did it. It wasn't until "epstein didnt kill himself" became a meme that people started to confound the conspiracy.
You dont have to bring them to court with it for it to be useful. It could be used to target individuals then they use more conventional methods of evidence gathering to arrest.
I would guess they arent currently doing it enmasse because that doesnt sound useful either. I would say, solely on a vibes based level its been done by US intelligence. Its really not so different than a wiretap.