Letting the “Kat” Out of the Bag? What to Make of Dealing with Cooperating Witnesses

As the Elizabeth "Lizzi" Marriott N.H. murder case with all its lurid details enters its final day of trial, a review of the court docket shows that Katherine "Kat" McDonough, the ex-girlfriend of accused murderer Seth Mazzaglia, spent 10 days on the stand testifying about their relationship with Marriott, her murder, the cover-up, and McDonough's self-professed role in all of it. Whatever the jury determines her role may have been, any potential punishment for what she may have done has been significantly reduced through her agreement to testify for the prosecution as a cooperating witness. McDonough, who otherwise could be charged with the same crimes (rape and first degree murder), and face the same penalties (life in prison without parole) as Mazzaglia is now only facing a maximum prison sentence of 3 years (so long as she lives up to her end of the "bargain") as a result of her cooperation and testimony against Mazzaglia.

As a longtime Boston-based criminal defense attorney who has often had to confront cooperating witnesses in open court, I can tell you that these cooperating witness plea deals are not only not out of the ordinary, but often a necessary "Hobbesian choice" to help the prosecution try to obtain guilty verdicts, especially in cases that are either circumstantial at best or otherwise devoid of eyewitness testimony. Offering a criminal a lower sentence in exchange for favorable information and testimony to convict a "bigger fish" may not, on its face, be a popular choice with the general public. However, as a former state and federal prosecutor, too, I can attest that it is sometimes a "necessary evil" that is a fact of life in the criminal justice system; the test of just how necessary, though, is often a topic of hot debate, a case-in-point being the deal federal prosecutors gave to John Martorano (regarding his 19 admitted murders) in exchange for his testimony against Whitey Bulger. Needless to say, the potential for deals of that nature, or along the lines we are now seeing in the Mazzaglia case, to backfire or blow-back on the prosecution is significant.

Putting my defense attorney "hat" back on, I can't argue with McDonough's decision to take the deal she was ultimately offered. If I were her lawyer, I would likely have advised her to do the same thing, since the controlling objective for any defense attorney is to protect and enforce the client's best interests. However, the flip-side to this consideration is what does Mazzaglia's trial lawyer do to try to combat the testimony of a cooperator like McDonough?

Having been in a situation of needing to impeach cooperating prosecution witnesses against my own defense clients numerous times during my many years of experience in courts, not just here in Massachusetts, but around the country, I can say, were I representing Mazzaglia, you would see me attacking McDonough's credibility at every turn, particularly since NH is a state whose procedural rules give defense attorneys an advantage in providing for a deposition process in criminal cases. This allows defense counsel to pin down a witness's prospective testimony ahead of time, before trial; I would try to later jam her up with that any time her trial testimony deviated from her original depo testimony. I would also emphasize how much her story has "evolved" or how different it is from what she originally said under oath during that earlier proceeding. In addition, in my cross-examination I would hammer home the fact that she "sold" her testimony to the prosecution by taking a deal in exchange for her cooperation and (throwing my defense attorney role right back at her) is simply looking out for her own best interests. I would repeatedly show how those motivations have "colored" her testimony and casts it into an entirely different light; that of a canary singing for its supper. I'd do all this to try to persuade the jury to question both the cooperator's credibility in terms of what she is "selling," and the prosecutor's in terms of what he is "buying" (with the deal he made) in hopes it will amount to more than enough reasonable doubt for the jury to return not guilty verdicts.

We saw the defense work hard to undermine McDonough's credibility through a nice job of cross-examination by Mazzaglia's attorney, and through his questioning of other witnesses as the defense team tried to shore up any weaknesses they felt may have lingered after the prosecution's case. The defense will have one more chance to comment on McDonough's cooperation and credibility in closing arguments later today, and you can be sure they will! However, we won't know until the final verdict is announced whether or not McDonough (and the prosecution) made the right call in taking a deal as a cooperating witness. Either way, McDonough is going to spend time in jail for her role in Lizzi Marriott's death. The question is, will Mazzaglia join her? Only the jury can determine what weight to give her testimony; whether she was a credible witness who told the truth during her lengthy testimony, or if this particular Kat was just trying to save her own tail.