"Witness tampering" and "obstruction of justice"

From Josh Marshall's TalkingPointsMemo:

Newsweek: McCain camp and its Alaska allies move to shut down trooper-gate probe.

Definitely take a look at the Newsweek article. Also take note of the following, that we're going to be looking into next week. Within days of Palin's selection, at least seven of her aides and associates, who had previously agreed to cooperate with the trooper-gate investigation, informed investigator Steve Branchflower that they were now no longer willing to be deposed. Note too that this was immediately after the McCain team deployed what George Stephanopoulos reported was a "rapid response team of about ten operatives that includes lawyers" to the state.

So the question is: what contact did representatives of the McCain campaign have with these aides that had agreed to testify but within days of her selection took back their pledge and are now refusing to cooperate?

From the U.S. Code, Chapter 73 (the "Obstruction of Justice" chapter), "witness tampering" [18 USC § 1512]:

(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 [...]

shall be fined under this title or imprisoned not more
than ten years, or both.

Time for a special prosecutor?