I understand at that point (initially) a person has not been read his rights, but if he waives his rights and signs a confession that is not coerced are you telling me the authorities cannot use it, nor use any of the evidence he willingly brought in? I have a hard time believing that because if that were the case all any criminal would have to do is bring all the evidence of his crime to the police and they couldn't prosecute him. "Here Sgt. McClusky, here's every shred of evidence you need to throw me in jail for life, but since I brought it to you myself rather than you having to investigate to find it you can't use any of it!"
Nevertheless, reporting a crime to the authorities is not the same as going public through public forums, and that's what we are talking about here. Going public through public forums doesn't mean the accussed has to testify at trial - he's still protected from doing that - but it does not mean whatever he said or did on camera is inadmissable.