TAMPERING WITH A WITNESS
Title 18, U.S.C., Sec. 1512, makes it a Federal crime or offense for anyone to use intimidation or physical force to threaten another person with intent to influence the testimony of a witness in any Court proceeding.
A person can be found guilty of that offense only if all of the following facts are proved beyond a reasonable doubt: First: That the witness was scheduled to be a witness in court; Second: That the person used intimidation/physical force against such witness; and Third: That the person did so knowingly and willfully with the intent to influence the testimony of the witness.
To act with intent to "influence" the testimony of a witness means to act for the purpose of getting the witness to change or color or shade his or her testimony in some way; but it is not necessary to prove that the witness' testimony was, in fact, changed in any way.