Prosecution’s use of noncustodial silence did not violate the Fifth Amendment. Petitioner, who was not in custody and had received no Miranda warnings, answered some of a police officer’s questions about a murder, but became silent when asked if testing would show that his shotgun matched the casings at the scene of the murder. Over his objection, the prosecution used his failure to answer the question as evidence of guilt. The United States Supreme Court affirmed the lower courts’ rulings affirming the conviction, rejecting petitioner’s claim that the prosecution’s use of his silence violated the Fifth Amendment. A plurality of the court concluded that the Fifth Amendment claim failed because Salinas did not expressly invoke the privilege in response to the officer’s question. A witness who desires the protection of the privilege must claim it at the time he relies on it. An exception to that requirement is that a defendant need not take the stand and assert the privilege at his own trial. Here, petitioner’s silence falls outside the exception because he had no comparable unqualified right not to speak during police questioning. A second exception is where government coercion makes his forfeiture of the privilege involuntary. This was not the case here because petitioner agreed to accompany officers to the station and was free to leave. The express invocation requirement applies even when an official has reason to suspect that the answer to the question could incriminate the witness. The Fifth Amendment guarantees that no one may be compelled in a criminal case to be a witness against himself, not an unqualified right to remain silent. Forfeiture of the privilege against self-incrimination need not be knowing.