18 U.S.C. § 1512 : US Code - Section 1512: Tampering with a witness, victim, or an informant

      (a)(1) Whoever kills or attempts to kill another person, with
    intent to - 
        (A) prevent the attendance or testimony of any person in an
      official proceeding;
        (B) prevent the production of a record, document, or other
      object, in an official proceeding; or
        (C) prevent the communication by any person to a law
      enforcement officer or judge of the United States of information
      relating to the commission or possible commission of a Federal
      offense or a violation of conditions of probation, parole, or
      release pending judicial proceedings;

    shall be punished as provided in paragraph (3).
      (2) Whoever uses physical force or the threat of physical force
    against any person, or attempts to do so, with intent to - 
        (A) influence, delay, or prevent the testimony of any person in
      an official proceeding;
        (B) cause or induce any person to - 
          (i) withhold testimony, or withhold a record, document, or
        other object, from an official proceeding;
          (ii) alter, destroy, mutilate, or conceal an object with
        intent to impair the integrity or availability of the object
        for use in an official proceeding;
          (iii) evade legal process summoning that person to appear as
        a witness, or to produce a record, document, or other object,
        in an official proceeding; or
          (iv) be absent from an official proceeding to which that
        person has been summoned by legal process; or

        (C) hinder, delay, or prevent the communication to a law
      enforcement officer or judge of the United States of information
      relating to the commission or possible commission of a Federal
      offense or a violation of conditions of probation, supervised
      release, parole, or release pending judicial proceedings;

    shall be punished as provided in paragraph (3).
      (3) The punishment for an offense under this subsection is - 
        (A) in the case of a killing, the punishment provided in
      sections 1111 and 1112;
        (B) in the case of - 
          (i) an attempt to murder; or
          (ii) the use or attempted use of physical force against any
        person;

      imprisonment for not more than 30 years; and
        (C) in the case of the threat of use of physical force against
      any person, imprisonment for not more than 20 years.

      (b) Whoever knowingly uses intimidation, threatens, or corruptly
    persuades another person, or attempts to do so, or engages in
    misleading conduct toward another person, with intent to - 
        (1) influence, delay, or prevent the testimony of any person in
      an official proceeding;
        (2) cause or induce any person to - 
          (A) withhold testimony, or withhold a record, document, or
        other object, from an official proceeding;
          (B) alter, destroy, mutilate, or conceal an object with
        intent to impair the object's integrity or availability for use
        in an official proceeding;
          (C) evade legal process summoning that person to appear as a
        witness, or to produce a record, document, or other object, in
        an official proceeding; or
          (D) be absent from an official proceeding to which such
        person has been summoned by legal process; or

        (3) hinder, delay, or prevent the communication to a law
      enforcement officer or judge of the United States of information
      relating to the commission or possible commission of a Federal
      offense or a violation of conditions of probation (!1) supervised
      release,,(!1) parole, or release pending judicial proceedings;


    shall be fined under this title or imprisoned not more than 20
    years, or both.
      (c) Whoever corruptly - 
        (1) alters, destroys, mutilates, or conceals a record,
      document, or other object, or attempts to do so, with the intent
      to impair the object's integrity or availability for use in an
      official proceeding; or
        (2) otherwise obstructs, influences, or impedes any official
      proceeding, or attempts to do so,

    shall be fined under this title or imprisoned not more than 20
    years, or both.
      (d) Whoever intentionally harasses another person and thereby
    hinders, delays, prevents, or dissuades any person from - 
        (1) attending or testifying in an official proceeding;
        (2) reporting to a law enforcement officer or judge of the
      United States the commission or possible commission of a Federal
      offense or a violation of conditions of probation (!1) supervised
      release,,(!1) parole, or release pending judicial proceedings;
        (3) arresting or seeking the arrest of another person in
      connection with a Federal offense; or
        (4) causing a criminal prosecution, or a parole or probation
      revocation proceeding, to be sought or instituted, or assisting
      in such prosecution or proceeding;

    or attempts to do so, shall be fined under this title or imprisoned
    not more than 3 years, or both.
      (e) In a prosecution for an offense under this section, it is an
    affirmative defense, as to which the defendant has the burden of
    proof by a preponderance of the evidence, that the conduct
    consisted solely of lawful conduct and that the defendant's sole
    intention was to encourage, induce, or cause the other person to
    testify truthfully.
      (f) For the purposes of this section - 
        (1) an official proceeding need not be pending or about to be
      instituted at the time of the offense; and
        (2) the testimony, or the record, document, or other object
      need not be admissible in evidence or free of a claim of
      privilege.

      (g) In a prosecution for an offense under this section, no state
    of mind need be proved with respect to the circumstance - 
        (1) that the official proceeding before a judge, court,
      magistrate judge, grand jury, or government agency is before a
      judge or court of the United States, a United States magistrate
      judge, a bankruptcy judge, a Federal grand jury, or a Federal
      Government agency; or
        (2) that the judge is a judge of the United States or that the
      law enforcement officer is an officer or employee of the Federal
      Government or a person authorized to act for or on behalf of the
      Federal Government or serving the Federal Government as an
      adviser or consultant.

      (h) There is extraterritorial Federal jurisdiction over an
    offense under this section.
      (i) A prosecution under this section or section 1503 may be
    brought in the district in which the official proceeding (whether
    or not pending or about to be instituted) was intended to be
    affected or in the district in which the conduct constituting the
    alleged offense occurred.
      (j) If the offense under this section occurs in connection with a
    trial of a criminal case, the maximum term of imprisonment which
    may be imposed for the offense shall be the higher of that
    otherwise provided by law or the maximum term that could have been
    imposed for any offense charged in such case.
      (k) Whoever conspires to commit any offense under this section
    shall be subject to the same penalties as those prescribed for the
    offense the commission of which was the object of the conspiracy.