I completely agree with you. The cop body cams protect everyone, both themselves and the other person/people they're recording. Goes both ways and I'm happy to see them wearing them as well.
The thing is, IF Jubelin had illegally recorded a person who ended up admitting during said recording, to killing W or taking him or some horrible thing, the fact GJ recorded him outside the boundaries of the law could easily completely screw up the criminal case against said person, and thereby risk the entire case, allowing that person to go free.
An experienced defence lawyer would fight tooth and nail to have that removed from evidence and if that was the only time the person admitted it and there was not much else to hang him on, we likely wouldn't even be allowed to hear about it, let alone ever see a conviction. And GJ is certainly experienced enough to know very well how things work. Again, the laws and requirement to obtain warrants when police want to bug and record people are there to protect both sides, not just the suspect from having his privacy invaded. All GJ needed to do was to renew his warrant and include his cellphone as one of the included devices, stating the reason of bad reception otherwise. Seems simple enough.
It almost seems like PS is on trial here without his presence or ability to defend himself, rather than getting to the main point that a very experienced cop put the entire case at risk. imo.