Perjury trap doctrine refers to a principle that a perjury indictment against a person must be dismissed if the prosecution secures it by calling that person as a grand-jury witness in an effort to obtain evidence for a perjury charge especially when the person’s testimony does not relate to issues material to the ongoing grand-jury investigation. The perjury trap is a form of entrapment defense, and so must be affirmatively proven by the defendant.
The following are examples of some case law on perjury trap:
A perjury trap is created when the government calls a witness before the grand jury for the primary purpose of obtaining testimony from him in order to prosecute him later for perjury. When testimony is elicited before a grand jury that is attempting to obtain useful information in furtherance of its investigation, or conducting a legitimate investigation into crimes which had in fact taken place within its jurisdiction, the perjury trap doctrine is, by definition, inapplicable. [United States v. Chen, 933 F.2d 793 (9th Cir. Guam 1991)]
The phrase ‘perjury trap’ suggests the deliberate use of a judicial proceeding to secure perjured testimony, a concept in itself abhorant.[United States v. Simone, 627 F. Supp. 1264, 1268 (D.N.J. 1986)]