Miranda v. Arizona, 384 U.S. 436 (1966) is commonly misunderstood. The statement of the accused may be used at trial so long as the accused was not in custody and also not protected from waiving the right to remain silent. This rule is subject to exceptions and the effect of this rule may be changed by other rules. The point I am trying to make is that to have a Miranda violation, you have to have the accused being (1)questioned while in (2)custody. If a person runs up to a strange cop on the beat and the cop asks "What's the matter with you? Did you do something wrong?" and the cop does nothing to indicate that the person has to stay to talk, and the person confesses to a crime, then that what the person says can be used at trial. Why? No custody. Another hypothetical: a person is arrested for overdue traffic tickets. That person speaks no English and none of the arresting officers speak the arrestee's language. They put the arrestee in a cell while they look for a translator. While waiting in jail, unable to communicate with anyone, he uses toilet paper to write out a murder confession in the language that none of the cops can figure out. When a translator is eventually found, Miranda does not keep this confession from being used at trial. Why? No questioning.
One more thing- Miranda warnings are not required for videos of the accused to be introduced showing that defendant couldn't walk or hit somebody. It's not needed for handwriting samples. It's not the reason warrants are sometimes required for blood samples. Thanks for Jamie Spencer of the Austin Criminal Defense Lawyer blog for pointing out the broad popular misunderstanding of Miranda.