"I guess this woman could implicate him but how credible is she?"
What does it matter? If the trial is before a judge only, the judge will have made his decision ahead of time (remember Collin Finnerty in DC); the trial will be for show, the sentence will be meant to intimidate and pressure the taxi driver over his testimony.
That is a felony--
Title 18 U.S.C. § 1512. Tampering with a witness, victim, or an informant--
(b) Whoever knowingly uses intimidation or physical force, or threatens 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: shall be fined ... or imprisoned ... or both.
Title 18 U.S.C. § 1513. Retaliating against a witness, victim, or an informant.
(a) Whoever knowingly engages in any conduct and thereby causes bodily injury to another person or damages the tangible property of another person, or threatens to do so, with intent to retaliate against any person for--
(1) the attendance of a witness or party at an official proceeding, or any testimony given or any record, document, or other object produced by a witness in an official proceeding; or
(2) any information relating to the commission or possible commission of a Federal offense.
Write your senators and congressmen NOW, and demand the FBI get involved in this mess.
Well, who is the judge? That's the question. If you get a judge like the one who acquited Flannery on the noise charge, then there's hope. If you get a judge like Stephens, Titus or Bushfan there may be a problem.