Graystar,
After reading, rereading, and rerereading this thread, I'm convinced that you're simply disregarding any answer that does not jibe with your pet theory of how this whole thing works. I'll try it one last time, more for the benefit of the audience than for the potential of educating you.
1. If police perform a custodial interview of a suspect, they must advise suspect of their rights, a la Miranda. A custodial interview is (roughly) defined as any situation where you are asking the suspect questions about a crime and that person is in a position where a reasonable person would not feel that they have the right to just get up and walk away.
2. If the police are performing an interview of a non-suspect, and he says something that suddenly leads them to think this guy might be a suspect AND the situation is one that a reasonable person would not feel that they had the right to just get up and walk away, this whole thing is suddenly transformed into a custodial interview. See #1.
3. The Miranda warning is not carved in stone. One does not have to read it verbatim from a card or form, but the warning given must hit the key points outlined in the Miranda v Arizona decision. Furthermore, there is no constitutional requirement for a signature on a rights waiver or anything to that effect, but many departments choose to do it this way because it helps ensure that the rights are read properly and understood. This is not only helps make sure that suspects know their rights, but it also helps kill defense motions to throw out the admission.
4. All Mirdanda warnings and subsequent statements are subject to suppression motions by the defense. This is where the decision to videotape interviews, usage of signed rights waivers and a demonstration of understanding by the accused comes in very handy. Officers who do a seat-of-the-pants Miranda will have a fun time on the stand with any law school graduate pro bono public defender.
5. The purpose of the Miranda warning is to ensure that the suspect knows that he has certain rights (silence, attorney, ability to invoke at a later time). Once that warning is given, if he invokes, either now or later, the police must honor it, or the statement will get tossed.
6. The purpose of the warning is not to prevent the police from subsequently asking questions afterwards (unless the suspect invokes). Having read the rights waiver, if the suspect agrees to talk, the police can and darned well should be asking them questions about the crime. There is a great deal of case law in determining how much pressure they can place on the suspect, and discussion of that is beyond the scope of this thread. It also exceeds my level of expertise, so I'll leave that to trained interviewers (if we have any). Suffice it to say that there is more to it than "I read him his rights now it's game-on". That is patently, absurdly false, and if you insist on making assertions to that effect, I'll promptly ask you to produce evidence to back them up.
The point of Miranda is not to ensure a pleasant, let's-all-join-hands-and-sing-Kumbaya interview. The point of Miranda is to advise the accused that he can, at any time, shut his pie hole and request the services of a lawyer. No more, no less. The propriety of psychological coercion in interviews has zero to do with Miranda. The reading of rights in no way absolves the police of anything they might do afterwards.
Mike