Defense Speaks in Trial of Dad Accused of Son's Hot-Car Death

Justin Ross Harris, 35, who has pleaded not guilty to murdering his 22-month-old son in 2014, cried in court as his attorneys shared the moment he discovered his lifeless son in the back seat of his SUV.
4:59 | 10/05/16

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Transcript for Defense Speaks in Trial of Dad Accused of Son's Hot-Car Death
We have a lot to get to, first the latest on that hot car trial where a father is facing murder charges for leaving his son in a scorching SUV for hours and now video showing his reaction to the death is raising big questions and Steve osunsami has the details from the courtroom. Reporter: In court this morning, jurors will hear more from witnesses who saw the moment when Justin Ross Harris bailed into this parking lot on his way home from work. I heard the car coming, brakes screeching, yelling going on. Reporter: During opening statements Harris' attorney says this is when he discovers the lifeless body of his son in the backseat of his SUV still strapped in a rear facing car seat after more than seven hours in the hot car. That little boy, he loved more than anything. Cooper's debt was an accident. Reporter: He cried in court reliving the day charged with murder and second degree child cruelty pleading not guilty saying it was an accident. He has always acknowledged this was his fault, that he was responsible but what you're going to see during this trial is that responsible isn't the same thing as criminal. Reporter: But police are testifying that Harris didn't look remorseful and shared video from inside this police cruiser where they say he seemed more concerned about the air-conditioning than his dead son. Feels like I'm not getting -- The air is all the way up. He immediately complained about how hot it was in my vehicle. Reporter: Harris' attorneys point to another piece of video from the same cruiser. Oh, my god, oh, my god. Reporter: Prosecutors say Harris left his son to die on purpose because he wanted a child-free life and had been sexting with other women that day. They say he knew the heat could kill after watching videos online. A point his lawyers deny. You see a child left alone in a vehicle, please call 911. Reporter: Harris is now divorced but his ex-wife is expected to take the stand and share that she too thinks this was an accident. Our thanks to Steve osunsami for that report. Joining us now Nancy grace, the host of "Nancy grace" on hlm and, Nancy, so many dramatic moments in day one of testimony. What stood out most to you? Well, I find it very ironic that he, Justin Ross Harris started crying during his defense's opening statements when it stated over and over and over that when he saw and realized, realized his son was dead he never shed a tear. Another thing that struck me is this, maybe I'm projecting but I recently lost my father and I remember there in the hospital they said, okay, you can leave now and there was just something innate, I did not want to leave him. Justin Ross Harris had no problems leaving his child's body. He left him there and I find that very, very disturbing. A lot has been made of Justin Ross Harris' sexting including allegedly to an underage girl. Do I like that, no. I want to hold my nose at it but that does not a murderer make. What will be more probative or helping the state prove their case is if they can come through with what was alleged in some of the search warrants that he had actually been searching how long does it take an animal or a dog to die in a hot car. Was he searching a new life, child-free? And another thing, I drove that exact drive that he took that morning. He went into chick-fil-a with his son. Not a drive-through. They all saw the son, cooper, happy, laughing. Put him back in the car, he had less than two minutes to drive. What, he forgot his son was alive in two minutes? How can that be? It can't. You hit all the key pieces of evidence that we'll hear from the prosecution. Inner its of the defense you heard in Steve's report that Harris' ex-wife is going to take the stand. What do you think that will do to bolt ter the account? She's expected to say it is an accident and supports her ex-husband. Okay, this is what I would do. If I were the prosecution I would not call her and I'll tell you why. Because if you let the defense call her, then you'll have her on cross-examination. They kind of threw down the gauntlet and said, look, the state is not going to call her, we will. Okay, great, call her. I'd rather have her on cross-examination. What do I think of her? "A," she says she -- she doesn't believe this was intentional. It was an accident. That her husband that she knows so well would never have done that. Well, did he know he was with hookers? Did she know he was cheating? If she didn't know that much how does she know he won't lie to save his own skin? That's what I would argue. A lot coming up in the court case. Nancy grace, thanks so much for joining us, as always. Thank you.

This transcript has been automatically generated and may not be 100% accurate.

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