Prior acts of a witness may be elicited during the interrogation of the witness to impeach the truthfulness of a witness, but the acts so inquired into must in fact be probative of truthfulness.

BE & K Construction Co. v. N.L.R.B., 536 U.S. 516, 531 (2002) ("An example of such 'breathing space' protection is the requirement that a public official seeking compensatory damages for defamation prove by clear and convincing evidence that false statements were made with knowledge or reckless...In some trials of civil actions the claimant's burden of proof is to establish the facts essential to its claim by clear and convincing evidence.

United States v. Mitchell, 145 F.3d 572, 576 (3d Cir. 1998) (vacating judgment of conviction for conspiracy to commit and commission of Hobbs Act robbery, and use of and carrying a firearm during a crime of violence....A statement falls within the hearsay exception provided by Federal Rule of Evidence 803(2) only if the statement is related to a startling event or condition.

Fed. R. Evid. 609(a)(1) ("(a) General rule. For the purpose of attacking the character for truthfulness of a witness, (1) evidence that a witness other than an accused has been....If a conviction is offered to impeach a witness and the conviction is not for a crime that involves dishonesty or false statement, the conviction of the witness may be used to impeach the witness if the crime for which the witness was convicted is punishable by death or imprisonment for more than a year, if the crime the witness committed is probative of the truthfulness of the witness, and if the opponent fails to show that the risk of prejudice or other harm mentioned in Federal Rule of Evidence 403 outweighs the probative value of the conviction; but if the witness to be impeached is a criminal defendant, the prosecution bears the burden of showing that the probative value of the conviction outweighs the risk of prejudice to the defendant.