The prosecution wants to make sure the process by which the evidence was obtained is not truthfully presented, because, as often as not, that process will raise questions.
I remember a time when I would hear a band and then want to hear everything that sounded like it; I wanted it to feel like I was tapping into a thing, even if it wasn't.
Every one wants to command, and no one wants to obey; and this is owing to the absence of that wonderful brahmacharya system of yore. First, learn to obey. The command will come by itself. Always first learn to be a servant, and then you will be fit to be a master.