with the michigan valedictorian on trial for killing his mother. His ex-girlfriend pointed a picture inside the home before the murder. But which side does it help? Dan and nancy to weigh in on that.... See More
with the michigan valedictorian on trial for killing his mother. His ex-girlfriend pointed a picture inside the home before the murder. But which side does it help? Dan and nancy to weigh in on that. First, abc's john muller. Reporter: Chilling testimony from the ex-girlfriend of a former high school valedictorian, accused of brutally murdering his own mother. She believed her medication was sorcery and witchcraft. And therefore, it was evil. Reporter: Holly telling jurors ruth pyne was dangerous and delusional, assaulting her son, jeffrey esh, in the months before she was murdered. She had been storing knives in her headboard. She watched the religious channel. Reporter: Prosecutors say 22-year-old jeffrey pyne bludgeoned his mother to death in the family's michigan garage in may of 2011. They claim he was fueled by pent-up rage after years of abuse at the hands of a mentally ill mother. Who spent time in jail for abusing him. Troubling for the defense, the dramatic blisters on jeffrey pyne's hands.Urbing photos that jurors have seen over and over again. Pyne maintains he got the blisters throwing a wooden pallet at his job. Freeman spoke of jeffrey's fear for his 12-year-old sister being alone in the house with his mother. A fear she shared with jeffrey. I did not think it was a good idea for julia to ever be alone with ruth in the house. Reporter: Defense attorneys maintain jeffrey was not involved in any way with his mother's murder. Claiming a stranger or strangers likely attacked ruth pyne on that may day in 2011. For "good morning america," john muller, abc news, new york. Okay. Let's get more from our legal team, nancy grace, abrams, our legal analyst. Dan, let me begin with you. The ex-girlfriend, a prosecution witness. And establishes grounds for a motive. And can create sympathy for the defense. She is doing what the prosecution wanted, which is to lay the groundwork for their motive, which is this is a mother who is out of control, who is slowly descending. That she's off her medication. That he had been worried about it. He had been talking about it. But right. On the other hand, it provides something. If the jurors don't want to convict here, and they want to sort of think to themselves, i don't believe that reason -- i believe they have not proven their case beyond a reasonable doubt, this will be one of the things in the back of their minds when they say to themselves, I don't know if i want to convict this guy. Nancy, in the end, was she an effective witness for the prosecution? Well, here's the deal. It's six of one, half-dozen of another. Several of the witnesses we heard from this week and the last 24 hours, have really hurt the state. And the irony is, the state brought them on. Number one, the girlfriend you're talking about. She was a witness for the state. But the reality is, I think she'd help the defense by describing the home life. Not only that, she described how ruth pyne, the deceased was hoarding an arsenal of lives in her headboard, behind her in her bed. That she had gone off the deep end, was watching the religious televangelists 24/7. Walking around the house with a bible. Was angry because her 22-year-old son was having sex with his girlfriend. Everything was going haywire in the home. And we find out the dad, and the state's bringing this on, gentlem gentlemen, that the father, bernie pyne, is having an affair, behind his wife's back. He's lying to his wife and the girlfriend, saying the wife is in a catatonic state. Now, we're seeing motive by the husband, too. And I'm very, very surprised they brought in evidence by the girlfriend, the boy, the defendant, had lied to her. He was cheating on the girlfriend. That's badion evidence. That's reversible error. What were they thinking? How far does the judge go to tell the jto disregard all of the extraneous? Judges, all the time, tell -- they do. Nancy's right to be laughing. They do tell jurors all the time. Disregard this particular piece of evidence. But the truth is, they heard it. Best not to tell the jury because if you tell the jury, don't listen to that, then they really listen to . Yeah. And that's always a real challenge. And does become an issue later on, in appeal. We talked a lot about this case about the possibility. Nancy used the word jury nullification. That the jurors may ignore the judge's instructions here and find them simply not guilty. I think there's a way for them to say, within the judge's instructions, I don't believe they've proven this case beyond a reasonable doubt. Yes, I believe there's questions. Yes, I believe there's a lot of evidence that sure looks like he did it. But I think these jurors -- no dna. I think the jurors, it's the hands and the alibi, that are the key pieces of evidence here. And I think the jurors could come to the conclusion, that's not proven beyond a reasonable doubt. We only have 30 seconds. You think they have a strong position? I think it boils down to the little girl left in the home. And the jury is going to think that little girl, just 12 years old now, was going to be brutalized by this mom. And they're going to let him walk. They're going to think he's a hero. Nancy, dan, thank you very much.
This transcript has been automatically generated and may not be 100% accurate.