“He doesn’t have to be your lawyer”
WOW…a criminal confesses to the prosecutor and under your theory the prosecutor could not testify.
Actually, he can. There is no atty/client privilege and the hearsay exception of admission against interest would apply to allow the testimony in.
I don’t practive criminal law, but having helped daughter and son in law study for the Bar exams last year I reviewed all kinds of thinbgs I haven’t dealt with in 30+ years