No person, the Fifth Amendment promises, “shall be compelled in any criminal case to be a witness against himself.” What it means “to be a witness” against oneself has been largely settled in American law since at least 1910, when Justice Oliver Wendell Holmes wrote in United States v. Holt that “the prohibition of compelling a man in a criminal court to be witness against himself is a prohibition of the use of physical or moral compulsion to extort communications from him. . . .” From Holt, the general principle has been derived that the compulsion of physical, noncommunicative evidence from a defendant—such as a demonstration of the fitting of an article of cloth-ing, a handwriting exemplar, a blood sample, or even documents—does not trigger the protections of the Self-Incrimination Clause because compelling a defendant to produce such evidence does not compel the defendant to be a “witness.” 

This principle, however, is neither historically nor logically sound. In fact, when Justice Thurgood Marshall complained in 1973 that he could not “accept the notion that the Government can compel a man to cooperate affirmatively in securing incriminating evidence when that evidence could not be obtained without the cooperation of the suspect,” he was simply reiterating a position with a historical pedigree stretching back to the Framers’ earliest discussion of the language of the Fifth Amendment and to even older caselaw from England concerning the production of documents. The Self-Incrimination Clause bars the admission of compelled evidence, testimonial or otherwise. At the time the Fifth Amendment was ratified, there was no semantic difference between “being a witness” and “giving evidence,” and no such difference existed before that time either. 

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