The Sixth Amendment to the United States Constitution provides that those who are charged with criminal offenses have the right to counsel at all critical stages of a legal proceeding. Relatedly, the Fifth Amendment provides that no person can be compelled to be a witness against themselves in a criminal trial.
Thus, in the 1966 case, Miranda v. Arizona, the United States Supreme Court held that police must provide certain rights at the time of arrest. Primarily, officers are required to inform arrestees that they have the right to remain silent, that anything they say can be used against them, and that they are entitled to an attorney, even if they cannot afford one.
Miranda rights must be read to someone any time they are subject to “custodial interrogation.” While the term is subject to varying interpretations, to establish custodial interrogation, a defendant must show that they were in custody and that police made some statement that would be expected to elicit a response. If police officers do not provide Miranda warnings at the time of arrest, any statements that are made by the arrestee cannot be used in a criminal trial against them.