Courts may require witnesses to appear and give testimony in court. A privilege is an exception to this rule. Some privileges are actually a constitutional right. Privileges allow an individual to object to proposed testimony regarding communications that they had with a person in a confidential relationship. There are different privileges that are recognized under state and federal law.
In the United States government, executive privilege is the power claimed by the President of the United States and other members of the executive branch to resist certain subpoenas and other interventions by the legislative and judicial branches of government to access information and personnel relating to the executive branch. The Supreme Court confirmed the legitimacy of this doctrine in United States v. Nixon, but only to the extent of confirming that there is a qualified privilege. Once invoked, a presumption of privilege is established, requiring the prosecutor to make a "sufficient showing" that the "Presidential material" is "essential to the justice of the case" (418 U.S. at 713-14). Chief Justice Burger further stated that executive privilege would most effectively apply when the oversight of the executive would impair that branch's national security concerns. Chief Justice Burger, writing for the majority in US v. Nixon noted: "Whatever the nature of the privilege of confidentiality of Presidential communications in the exercise of Art. II powers, the privilege can be said to derive from the supremacy of each branch within its own assigned area of constitutional duties. Certain powers and privileges flow from the nature of enumerated powers; the protection of the confidentiality of Presidential communications has similar constitutional underpinnings." Because Nixon had asserted only a generalized need for confidentiality, the Court held that the larger public interest in obtaining the truth in the context of a criminal prosecution took precedence.
A privilege guaranteed by the Fifth Amendment to the Constitution bans a a witness from being compelled to give testimony that is self-incriminating. A witness in “any proceeding, civil or criminal, administrative or judicial, investigatory or adjudicatory” may assert the privilege against self-incrimination. Kastigar v. U.S., 406 U.S. 441, 444-45 (1972). The assertion must be related to the witness’s “reasonabl[e] belie[f] that the information sought, or discoverable as a result of his testimony, could be used in a subsequent . . . criminal proceeding.” U.S. v. Balsys, 524 U.S. 666, 672 (1999).
The privilege applies generally only to testimonial evidence. See, e.g., Oregon v. Elstad, 470 U.S. 298, 304 (1985) (“The Fifth Amendment, of course, is not concerned with nontestimonial evidence.”). Physical evidence is not testimonial. See, e.g., Commonwealth v. Conkey, 430 Mass. 139, 142 (1999) (“If evidence sought is real or physical evidence, such as hair and blood samples, voice exemplars, fingerprints, lineups, sobriety tests, or breathalyzer tests, art. 12 does not protect a person from having to provide such evidence.”). However, when admitted to show consciousness of guilt, conduct evidence is “always testimonial because it tends to demonstrate that the defendant knew he was guilty,” e.g., threat or intimidation of potential witness, attempt to commit suicide, refusal to turn over physical evidence, refusal to take field sobriety test, destruction of evidence, flight, altered appearance, and false statements. Id. at 142 (internal citations omitted).
If a witness testifies about incriminating matters and does not assert his privilege against self-incrimination, it is waived. U.S. v. Monia, 317 U.S. 424, 427 (1943). However, if a witness is compelled to testify, the witness has no reason to assert the privilege until “testimony sought to be elicited will in fact tend to incriminate.” Brown v. U.S., 356 U.S. 148, 156 (1958) (“He must be able to raise the bar at the point in his testimony when his immunity becomes operated.”).
“It is well-established that a witness, in a single proceeding, may not testify voluntarily about a subject and then invoke the privilege against self-incrimination when questioned about the details.” Mitchell v. U.S., 526 U.S. 314, 321 (1999); Brown v. U.S., 356 U.S. at 156 (witness cannot testify on her own behalf and then assert the privilege during cross examination “on matters raised by her own testimony on direct examination.”). A criminal defendant “has no right to set forth to [the factfinder] all the facts which tend in his favor without laying himself open to a cross examination upon those facts.” Brown, 356 U.S. at 155 (internal quotation omitted). When a witness testifies voluntarily, “certainly if he is a party, [he] determines the area of disclosure and therefore of inquiry.” Id. at 155-156. The witness, therefore, can face cross examination on those facts which he puts into dispute. Id.
If a witness waives his privilege in regard to a particular topic, he does not waive his privilege as to all possible related topics. See Rogers v. U.S., 340 U.S. 367, 373-374 (1951); Hashagan v. U.S., 283 F.2d 345, 352 (9th Cir. 1960). See generally 3 Nancy Hollander et al., Wharton’s Criminal Procedure, §20:12, at 20-46 – 20-49 (14th ed. 2008) (explaining precedent in regard to waiver and related topics). If a witness has testified regarding an incriminating matter, he has waived his privilege in regard to that matter; however, he has not waived the privilege in regard to testimony which might further incriminate him regarding other crimes. Hashagan, 283 F.2d at 354.