In United States v. Wood (1840) 39 U.S. 430, the defendant was charged with having sworn falsely to the United States customs department about the price of goods he had imported. To show the falsity of the oath, the government presented an invoice book belonging to the defendant's father and business partner, and letters written by the defendant to his father describing the intended fraud. The state fails to acknowledge that in Wood the United States Supreme Court carefully limited its holding to a case where the "documentary or written testimony springs from the defendant himself . . . ." (Id., 441.) That case shows that the rule, which forbids conviction on the unsupported testimony of one witness as to falsity of the matter alleged as perjury, does not relate to the kind or amount of other evidence required to establish that fact. Undoubtedly in some cases documents emanating from the accused and the attending circumstances may constitute better evidence of such falsity than any amount of oral testimony.