Miranda rights come from the 5th Amendment's Right to Remain Silent, along with a case by the United States Supreme Court, Miranda v. Arizonia, where the court held a defendant had to be advised of basic rights, including the right to remain silent. Defendants are cautioned that anything they say can and will be used against them in a court of law, which tends to be very true. Often times, an officer will secretly tape record the conversations for later use in court.
Because of Miranda v Arizona, failure of law enforcement to read the Miranda Rights usually results in any statements being supressed as involuntary, as long as the individual was detained (not free to leave) and being interrogated. This disctintion is routinely a heated debate in court, with the prosection arguing the defendant was not detained in order to alleviate the officer of reading miranda rights.
Interrogation is usually easy to show; as long as the officer is asking questions or seeking an admission, there is interrogation. However, showing detention typically requires more of an analysis. If a person is not being detained -- for instance, simply standing on the sidewalk while an officer asks questions -- then there is no need for an officer to read the miranda rights. However, if the individual is handcuffed, seated in the back of a squad car, and being questioned by three armed officers, then the court would generally find a detention, thereby requiring Miranda Rights to be read to the defendant.
As unlikely as it seems, many times an individual will blurt out a statement, before any question is posed. Such a statement is considered an excited utterance, and is exempt from the Miranda rights and 5th amendment law. Since the officer was not interrogating when the defendant made the statement, then it is admissable without a violation of the 5th amendment or Miranda rights.
If you found this helpful, the following guides may be useful:
Overview of Criminal Case Guide: Arrest | Arraignment | Pretrials | Motions | Jury Trial | Sentencing | Appeals
4th Amendment Rights: Warrants | Pat Down | Plain View Search | Search Incident to Arrest | Car Search | Consent | Bag Search | Home Search
Other Constitutional Protections: 5th Amendment Miranda Rights | 6th Amendment Right to Counsel