In the case of United States v. Mara, also known as Marasovich in 1972, the Supreme Court ruled on whether or not a grand jury witness could refuse to provide handwriting exemplars (samples) based on Fifth Amendment rights against self-incrimination. The court held that compelling a person to submit handwriting samples did not violate their Fifth Amendment rights because it was non-testimonial evidence and therefore didn't involve any communicative act or reveal any knowledge he might have had. It was merely an identifying physical characteristic outside the protection of the amendment, similar to providing fingerprints or voice recordings for identification purposes. This decision reaffirmed that while individuals cannot be compelled to testify against themselves under the Fifth Amendment, they can be required to provide physical evidence for use in investigations and prosecutions.

In the dissenting opinion for United States v. Mara, Justice Douglas argued that compelling a person to produce voice exemplars violated their Fifth Amendment rights against self-incrimination. He contended that the majority's decision expanded the scope of physical evidence beyond its original intent and blurred the line between testimonial and non-testimonial evidence. In his view, forcing someone to speak so their voice can be identified is not merely obtaining physical characteristics but rather extracting "words" from them which could potentially incriminate them in a crime - an act he believed was constitutionally protected under the Fifth Amendment.