The prohibition of compulsory self-incrimination has typically been applied not only to the defendant in a criminal trial, but rather to any witness who might be sworn to give testimony. Another practical problem arises from the right against self-incrimination: it can be a real hindrance to the police. Often, the very witnesses who are most likely to know “who done it” are themselves implicated in the crime. For this reason, prosecutors have long been willing to grant immunity from prosecution to some suspects in exchange for their unreserved testimony about other suspects. Statutes allowing immunity were first enacted in England in the early 18th century, and they were soon adopted in the colonies. Immunity statutes were adopted for federal courts in the second half of the 19th century.
The self-incrimination protection was applied to state courts in Malloy v. Hogan in 1964. In 1966, in a case with arguably even greater significance, the Court decided in Miranda v. Arizona that testimony acquired from police interrogation could not be used in court unless police first “inform accused persons of their right of silence” as well as other rights. Suspects must knowingly waive their right to remain silent before their testimony is deemed admissible in court. The necessity of reading every suspect his “Miranda rights” means that every person is now protected from compulsory self-incrimination even before he becomes a defendant in a criminal trial.