Transcript for Dramatic Testimony in 'Loud Music' Murder Trial
Today the defense started presenting its case in a murder trial that contains a combustible mix of race and guns and is playing out in the same state where trayvon martin died, Florida. The accused is a 47-year-old white software developer named Michael Dunn. The victim, an apparently unarmed black 17-year-old named Jordan Davis. The alleged motive? Loud rap music. ABC's Ryan Owens is on the story for our series "Crime and punishment." ♪ Reporter: Is it possible this rap song could be a motive for murder? ♪ Infrared, yeah, we love them ♪ possible that a 17-year-old is dead because he wouldn't turn down the volume? That's the stunning accusation of prosecutors in the state of Florida versus Michael Dunn. Michael David Dunn pointed a semi-automatic pistol at four unarmed kids from a distance much closer than you and I. And then drove off. Reporter: Police say the software developer fired ten shots at that SUV, killing Jordan Davis back in November of 2012. Prosecutors rested their case earlier today, ending with graphic testimony from the medical examiner. How many separate gunshot wounds did you find to Jordan Davis's body? Three gunshot wounds. Reporter: The M.E. Displayed Jordan Davis's clothes for the jury. The bullet-riddled tanktop, the blood-stained t-shirt. So right about here is where the bullet entered. Reporter: Noticeably absent for this testimony, Davis's parents. They've been here every day, but their civil attorney says they just couldn't sit through this. It wasn't until today that they decided that there's a line there and the photographs that came from that was across that line. It can't be easy for them to even be in the same room as the man who admits to killing their son. It's not. And it hasn't been for the past year. Reporter: They did watch in dramatic fashion as a firearms expert showed the jury the semi-automatic pistol that ended the teen's life. But the most powerful part of the prosecution's case came from a most unlikely source, Michael Dunn's fiancee. And what did the defendant say? "I hate that thug music." Reporter: Rhonda rouer testified those are the last words she heard her fiance say before he opened fire on the SUV parked right next to him. The couple had stopped at this Jacksonville gas station to buy wine after the wedding. She went inside. That's her on the store surveillance tape with a bottle of wine. Next, gunfire. Oh, my god, somebody's shooting. Somebody's shooting out of their car. I heard pop, pop, pop. Reporter: Rouer says she ran outside and Dunn told her to get back in the car. Did you see a firearm at that point in time? Yes. Michael was putting it into the glove box. Reporter: Prosecutors say Dunn hit the SUV nine times including several shots to the back of the vehicle as the driver was pulling away. Rouer was a reluctant witness for the prosecution, sobbing and shaking throughout her testimony that the state hopes will put her fiance away for life. She described how after the shooting Dunn left and never called for help. That instead they went to this hotel, ordered pizza, and shared more drinks. Rouer testified it was her idea to head back to their home in central Florida without telling a soul what happened. After seeing the reports of the teenager's death on the news. Why did you decide that you all needed to go home? Because I thought I was going to be arrested too. Reporter: When police did arrest Dunn the next day, he told officers he fired in self-defense. I was so afraid that I didn't have time to think. I only reacted. Reporter: That he felt threatened and thought he saw a weapon. It was either a barrel or a stick. But sir, there -- they're like, "We're going to kill you." Reporter: No weapon was ever found in the teenagers' car. Still, Dunn's attorney says Jordan Davis was the aggressor and threatened his client. "You're dead ." "This is going down now." With a shotgun barrel sticking out of the window. Or a lead pipe. Whatever it was, it's a deadly weapon. Reporter: This afternoon on day four of this high-profile trial the defense began its case. Calling character witnesses to say quite simply Dunn is a good guy. Are you aware of Mr. Dunn's reputation for peacefulness? Yes. Very nice guy. Reporter: The defendant's son, Chris Dunn, took the stand to defend his dad. He's my father. Reporter: The defense showed the jury wedding pictures from the night Chris got married. It was just after Michael Dunn left the reception that the shooting happened. Dunn himself has not commented publicly on his side of the story. But since being in jail he has written many letters. They've now been submitted as evidence. In a letter dated July 14th, presumably to his fiancee, he writes, "I just got off the phone with you and we were talking about how racist the blacks are up here. The more time I am exposed to these people the more prejudiced against them I become." In another letter to his grandmother he complains, "The blacks seem to be calling the shots in the media and the courts." In yet another letter he acknowledges comparisons to the trayvon martin shooting. "Cory, my attorney, says I have a much stronger case of self-defense than Zimmerman does." This case does seem to have a lot of parallels to the George Zimmerman trial. Right down to the prosecutors. Jordan Davis gasping for air. Reporter: These are the same two who tried to get a conviction against Zimmerman. I don't see how stand your ground applies there. But in this case, with Michael Dunn, it's just straight defense. How reasonable was he in reaching into his glove compartment, pulling out a 9-millimeter, and then pulling the trigger not once like George Zimmerman but two, three, four, ten times. Reporter: To make his defense stick, many legal experts believe Dunn needs to get up before this jury and explain what happened that night. The family wants answers. And only Michael Dunn can give those answers. So it seems odd, but they actually want to hear from their son's killer? They do. It's unfortunate in America that the young black child doesn't get the benefit of the doubt. Reporter: The defense says they only have one or two witnesses left. The question remains tonight, will Michael Dunn be one of them? I'm Ryan Owens for "Nightline" in Jacksonville, Florida.
This transcript has been automatically generated and may not be 100% accurate.