Transcript for Martin MacNeill's 12-Year-Old Daughter Takes the Stand
This is a special room. -- -- couple Cutler and New York with this ABC news digital special report the mistress now a witness they seventh testimony in the trial of Martin McNeal. You saw -- doctor charged with killing his wife ought to continue an affair the prosecution. Trying to show that Martin McNeal is untrustworthy and that he acted very suspiciously at the death of his wife Michelle. Later today the youngest daughter twelve year old -- McNeal is to take the stand against her father. But the day started off with the other woman Gypsy Willis who Martin brought in to be the children's nanny. How did he introduce you. Believe he and -- -- -- -- and what named it -- Chilean. And the to view resume your sexual relationship when you are moved into the home estimate. Yes. So for more on the trial wanna bring -- homicide prosecutor and a -- and a lot -- Anna -- thanks for being with us today that afternoon to some harsh. Testimony from Gypsy Willis how much will the jury -- the fact that -- and Gypsy had a relationship. And the way it strongly because that if you as you know is the prosecution's contention that is the motive here. She's a very interesting witness for the prosecution has not only issue the other woman to the jury already is looking at -- that she is the person who. Came into this marriage when no one else should have been there. And ultimately. Though she is a witness does the prosecution believe everything she says I think we can -- see today that they do not won -- last questions by the prosecutor to her was. You know ms. Willis after this very. Long ongoing close relationship not only emotionally but -- you moved into this man's home after wife was killed. Are you telling this jury that you know not thing. More about Michelle. -- -- stats and her answer was no singing I think that's important question because that is the prosecutors. Reminded the jury that we needed to call this witness. There is evidence they got from her they could only get from her against. Martin McNeal such as that this identity. Scam that the two of them created after Michelle's death to make her. -- now wife -- with the daughter's identity -- they create an identity they can only get that through her however the under current here is that if she wasn't involved she certainly knew -- this is because of her that the doctor killed his wife so it was very important quite riveting testimony from her today. -- what was interesting in its testimony is that in Gypsies cross an amateur cross examination the defense underscored. Her testimony as being truthful and I want to play some of that. And part of. Your deal with the prosecution. Is that you were required to testify truthfully in this in these proceedings strip. And if you didn't testify truthfully. You will -- you will have breached that part of your deal with them. Yes and you will be looking -- spending three years in prison yes. You also know that if you testify. Falsely -- could be charged with perjury yes. And spend up to fifteen years in the Utah state prison yes. And so and -- -- to ask about this and that that the jury won't just be dismissing Gypsies testimony if the stakes are about high is that -- Adam major determining factor. Thinks you know what the what the defense want to remind the jury is locking up the only questions we're going to ask this woman is you are telling the truth is that. Are you telling the truth yes if you lie you have a lot at stake you were given a deal you only get the deal if you testify honestly. You have potential perjury charges and could serve up to fifteen years. But I'm the prosecutor I'm easily -- monetary the end. Well -- you say that however if she admits to her. Involvement if she had not come forward the way that she had to give evidence against him -- we ultimately found out she was involved she could be facing the rest of her life. So it's easy to flip that to she's the type of witness that I would tell the jury you know you can believe certain things that she says. Because we have outside corroboration outside -- that is believable. But also you know take what she says with a grain of salt remember who she is she is a woman. Who was very happy to tell her friend at this relationship with the doctor was moving forward -- that things had changed and lost he had an innocent explanation today for that Jerry. I think we still should be in the jury may well suspect that there's more to -- this woman is not willing to implement. How heavily will the fact that she was convicted of identity theft play into this case it's the type of crime that a jury should always consider it's not. You know assaulting someone which while bad and illegal as a pretty direct one on one crimes something that someone is. Guilty of that involves deceit which fraud is that is willing to. Lie and deceive others really can affect their credibility and believe ability much more and so I think that is quite important to remember what her prior crimes are. In this case the judge has forbidden. Referring to Michelle marked the doctor's wife as a victim. Because the defense is claiming that no homicide in fact took place how does that -- effect the prosecution's maneuvering. I don't think it affects them very much to me clearly she is a victim this woman is dead and whether you want to ultimately if they side saying she's not guilty to the victim of a horrendous affair. And treatment by -- husband that certainly know is going to say was any good and that worsen with the prosecution contends she's the victim of murder. Because they can't use the word I don't think changes. It very much they are going to argued that the facts are very clear as to what she was and what this adds up to and it is murder. By her husband Martin -- Throughout this entire trot across he's been trying to show that Martin McNeal. He is untrustworthy. And fact that their latest issue -- faking the use of a -- in fact Michelle's sister Linda -- Testifies to that let's listen. At first. He wasn't -- McCain anyway Susan -- And and -- eight presents fat. Concerned he he picked up eight. From his first people weren't there. -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- You refer to him picking up -- where did you pick up beta -- Aaron. The plot area. -- Nationalists. Cast whereas K was he using his cane when he picked up beta now do you know what happened to -- -- was set aside. Okay that's not sitting there. Possibly the faking a leg injury -- line -- that cancer he also faked a college degree he allowed his daughter's identity stolen. I mean obviously those are things that are going against Martin -- but are they enough to convince the jury of murder. By himself no but again these are pieces of eight. Picture -- a puzzle -- the jury is slowly piecing together they're showing this man from the bottom up the smallest to the biggest. Who very easily moves in an out of the truth in an added to -- From you know running back and forth an -- came -- people cannot see him at his wife's funeral -- -- very quickly hobbling around on McCain. Ultimately the biggest deception which is creating and suppose it accident. Or -- natural. -- demise of his wife when in fact to use his medical skills to kill her with those drugs and drowned her in a bathtub that's that the jury is. Going to hear from the prosecution the end -- from the ground up -- every -- points this man's guilt to ultimately he was willing to murder and his. In deceiving everyone threw out. And right now the juries listen to testimony from Ada these six year old daughter as an excuse me she's not twelve years bush was six at the time that is the time this interview was conducted. The judge though has not allowed her to testify -- she will be cross examined. How exactly does that work. When it comes to child witnesses the -- the rules are much broader in scope because they aren't like adults and hear the judge said that she is important testimony to give she is the one who was with her father. When they came home she is the one who found her mother's lifeless body in the bathtub -- that that's important for the jury here however he also found. That she had certain. -- 11 year later in 2008. For the jury to hear that and that then the defense can cross examine her on that so he wants her testimony. To be as most accurate as truthful so he believes the judge ruled without be closer in time so it's unusual ruling. But a lot of times there is room for more discretion when it comes to a child -- So the statement was made when she was six years old she is now twelve I mean how crucial are those comments going to be will the jury value at less. Given her age consideration. It depends on the child you know. When you think of certain children there are ones that when they speak to you know that they know exactly what they're talking -- 616 or 26 in their other ones. Based on the way they speak in the way they conduct themselves that he might have more doubts that's really going to depend how she. Sounds and how she appears remember -- a video audio statement. How she sounds to them and how she presents herself on the stand I think it's going to be important and the jury will weigh up because again she is the child and not just. Michelle -- but also. -- she's meet Michelle McNeill but Martin McNeil as well and so. You would think that she comes into this without an interest that they will be looking very carefully at what she has to say about how her father acted. About how was that her mother's body was positioned when they found hair. Now it -- his relationship though is slightly complicated she is the biological granddaughter of Martin McNeal who then was put in the custody. Of her adopted a line is that how I understand the. And you know there's a lot of but nuances in these fans in this family here that are are not the usual but you know I think what we have to remember is that she grew up with him as her. Father she was six -- to a six year old it doesn't matter where the -- Biological. Adopted or not it is your character -- the person is postal loving care. You know whether you you were born from them or not so I think they're going to be looking at her and her testimony coming from a child period of this man and Michel Martin. All right and of course the testimony will continue in that case and -- -- get thank you for your time and your insight today. Yeah we do have a complete report right here on abcnews.com. For now I'm -- Cutler in New York with the CBC news digital special report.
This transcript has been automatically generated and may not be 100% accurate.