Transcript for Medical Examiner Calls Zimmerman Injuries 'Insignificant'
george zimmerman trial. Stakes never higher. Trayvon martin's parents could testify as early as today. And matt gutman on the prosecution's struggle to make their case. Good morning to you. Reporter: Good morning, josh. That's right. For the past few days, the prosecution's case has been limping along. There is no smoking gun. The witnesses they put on the stand has turned against them. And the only person who knows exactly what happened that night, george zimmerman, is not likely to talk. The prosecution has been hammering away where it can, george zimmerman's credibility. After seven days of testimony, the prosecution came out swinging. I'm hitting you, correct? Reporter: Bringing in this medical examiner to dismantle zimmerman's claim that he was in a life-or-death struggle with 17-year-old trayvon martin. How would you classify the injuries to the defendant's head? They were not life-threatening. They were insignificant. Reporter: And the prosecution sliding away zimmerman's credibility. Using his own words in this call to police that night against him. . On the stand, the lead investigator who recommended manslaughter charges against zimmerman, weighing in, bolstering the prosecution's point. In your opinion, calling somebody, referencing as, pardon me my language, punks. That is a little in spite. It is? Reporter: The wording there, critical. As the prosecution told jurors, demonstrating ill will or spite is critical for a second-degree murder conviction. After court, zimmerman's lead attorney, mark o'mara, whose client says he shot martin in self-defense, says the case is undented. Self-defense is you have reasonable fear of future bodily injury. Under the statute, you don't have to get hit once for self-defense to exist. Reporter: But the prosecution attacking zimmerman's team outside the courtroom, as well. At issue, this photograph, posted on instagram by defense attorney don west's daughter. It has the caption, we beat stupid celebration cones. The prosecution going after the defense late tuesday, saying the caption transferred to trayvon martin's friend, rachel jeantel, who was grilled on the stand last week. I don't read cursive. Reporter: The prosecution filed the motion, it wants to ensure that witnesses and court proceedings are treated with respect. That's important because we could see eight more witnesses take the stand. And it's expected the prosecution will try to end this case in the way it started, by tugging at the heart strings of those six female jurors. Look to see trayvon martin's mother, who has been in court day after day, to be the last person to take the stand. Matt gutman in sanford. We want to turn to abc's chief legal affairs anchor, dan abrams, also reporting on the trial in sanford. A bit of interesting -- interesting start to tuesday's proceedings, when the judge struck out something that a prosecution witness had said. But you don't believe it actually helped the prosecution when it was done. Well, first of all, think about the fact that prosecutors are asking that a statement from one of their own witnesses be struck. But beyond that, you have the fact that you can't unring the bell, right? The jurors have heard this. The first thing they hear when they arrive that morning is don't pay attention to that really, really important, big thing that was said at the end of court yesterday. That in and of itself is a problem for prosecutors. So, the prosecutors had to make a tough decision. Do we make a big deal about this and ask that it be stricken, as they did. Or do we just hope it fades into the background? They realized it was so important and so big, that they would still be willing to have the judge give that instruction and highlight it again. Dan, the prosecution, once again, spending a lot of time trying to highlight inconsistencies in zimmerman's various accounts. How well did it do? It's their best argument here. I mean, their best case is george zimmerman's story doesn't make sense. The problem is, the inconsistencies they're talking about are relatively minor compared to the consistency of the major issues in george zimmerman's account. I think that is the reason we will not see george zimmerman take the stand. His team believes that those inconsistencies that have been brought up again and again in court, are just not that big a deal. And yet, we do expect to hear from trayvon martin's parents. Both could perhaps be testifying as early as today. Certainly, an emotional day. Dan abram, thanks for your time
This transcript has been automatically generated and may not be 100% accurate.