Could any parent ever do this on purpose . Inside this landmark case. He was everything to me. Everything was taken away from her. Her whole life has changed. A heartbreaking family tragedy. Was it an accident or a crime . She knew what the truth was. There were a whole lot of secrets to be revealed. Yes, maam. Im lester holt. And this is dateline. Heres Andrea Canning with unimaginable. Reporter youre watching as a Police Cruiser races to an atlanta parking lot. A call for help has come over the radio. Child not breathing. Hed been found in the back seat of a hot car. Every year an average of 37 children die from heatstroke after being forgotten or left behind in cars in the heat of the sun. And parents pay the ultimate price for lives that are busy, distracted, sometimes overwhelming. Police werent able to save 22monthold Cooper Harris a few years eeg ago, and his death in hot car made headlines nationwide. New details in a tragic case weve been following, the death of a georgia toddler. Reporter but there was Something Different about coopers story. Something darker. Because coopers dad, ross harris, ended up being charged with a crime. Accused not of forgetting cooper but of murdering him. And his murder weapon of choice, prosecutors said, was a hot car. But even if youve seen the headlines, theres a lot more to this story you may not know. Tonight well take you to the scene, show you Surveillance Footage from that day and give you an indepth look at the evidence. It sent chills down our spines knowing we were in th reporter well also talk to insiders who have never spoken out before. They say ross harris was not a killer but a doting dad. Was he a proud dad . So proud. He loved that boy. Reporter a father who ended up on trial for an unimaginable crime. The entire case was a house of cards. Reporter and just like the people around him, you can decide is this the face of a dad who just made the worst mistake of his life . Or a murderer . Oh, my god. What have i done . Reporter ross harris grew up in tuscaloosa, alabama, and thats where his close friend, billy kirkpatrick, met him. You called him a massive dork . Massive dork, yes. Reporter why did you call him that . Because hes a massive dork. A lot of fun to be around. He remembers one beach holiday in particular. Ross took his guitar and, like, walked up to people on the beach and started conversations because thats who he is. Reporter was he playing for them, too . He was. They didnt ask him to. But he was playing. Reporter but ross seemed to settle down when he met his wife, leanna. She encouraged him to get his college degree. His cousin katie, who quickly became leannas best friend too, says leanna made ross want to be a better man. Weve said that without leanna, ross wouldve probably been a lost little, puppy. Reporter after six years of marriage, they moved to atlanta when ross was offered a job as a Web Developer at home depot. Cooper was born a few months later. What was it like for you, the first time that you that you saw cooper . Oh, man, he was so beautiful, just blonde hair, blue eyes. Just tiny little perfection. I just had this vision of, you know, ross andoo couch and ross is just goofing around with him and get on the floor with him. And its hilarious. Any extra thing that cooper could do, any milestone that he hit, he would share it with everyone. One of the conversations i had with ross, he said that it was so cool that cooper knew his name. And he said, and he loves to yell it at me. So instead of saying dad. He would just go ross. And he would yell ross at him all the time. Reporter it was ross who took cooper to day care most mornings. And that was where leanna expected to pick him up on june 18th, 2014. Here she is arriving at the day care. She got to the day care and cooper wasnt there. Reporter leanna called ross to see if there had been a mixup, but he didnt pick up. And then she had a worrying thought maybe ross had accidentally left cooper at home. She texted her neighbor and asked her to just go look. She has a key to her apartment. Just go look. See if hes there. And she was like, maybe the house will just be torn up. It had be a little toddler tornado when she gets there, but hell be there. Obviously, he wasnt. Reporter leanna rushed over to ross office to see if cooper was there. It was at home depot that a Police Officer tracked her down. Their conversation was recorded as he gave her the worst possible news. There aint no easy way to tell you this. Your child is deceased. Im very sorry to have to tell you that. Where is my husband . Your husband is up at our headquarters right now. Reporter the officer explained ross had never taken cooper to day care that day. That hed done the unthinkable, and left cooper in his car for seven hours in the georgia heat. Has he ever done anything like that, forgetting about no. Do you know what might have made him forget about it . No. I think any parent could put themselves in that situation with their own child. And its so hard to fathom being in a place like that. I think she was in full denial, like, that it wasnt happening. It was a nightmare, is what she said. Im going to wake up and it will be fine. This didnt happen. Reporter leanna was taken to the Cobb County Police headquarters. Ross was already there in an Interview Room, telling detectives what had happened. But to them, something about ross harris and his story wasnt adding up. What really happen that morning . When we come back oh, please, god, why . I didnt mean to. I know you didnt, baby. I know you didnt. Questions about a fathers story. The antennas went up on the detectives when they heard that. And rewards points on all prescriptions, walgreens has you covered. So drop by and seize the savings walgreens. At the corner of happy and healthy. Hdid you get that email i sente wyou. Before you wake up. When life keeps you up. Zzzquil helps you fall asleep in less than 20 minutes. Because sleep is a beautiful thing. Ahyou the law . Weve had some complaints of. Is that a fire . Theres your payoff, deputy. Git velveeta shells cheese. Theres gold in them thar shells. Oohh look a hungry dinosaur muum dinosaurs only eat meat actually the biggest dinosaurs only ate plants country crock has always been made with the goodness of plants. It has real, simple ingredients. And that same delicious taste you love. Real Country Fresh taste, made with the goodness of plants. Welcome to crock country. Ross harris sat alone in the place they call the box, an Interview Room at the Cobb County Police department. Oh, please, god, why . Reporter he could barely keep still as he waited for detectives to question him about the death of his son cooper. He had a horrible story to tell. Ross, just kind of run me through your morning today. Reporter prosecutor chuck boring was brought into the investigation early on. I think the main goal in a case like this is to get a timeline of the events. Reporter ross told detectives the morning had begun like many others. Leanna set off to work early. Ross set out to take cooper to day care and decided to stop for breakfast at chickfila near his office. And me and him do that at chickfila in vinings approximately two or three times a month together. Reporter after they ate, ross said he strapped cooper into his car seat. I gave him a kiss. He gave me a kiss. What i do every time. Its my routine. And just today was just like, careless. I got in my car, and instead of reporter ross told police hed simply forgotten to take cooper to day care. I went to work. As if he wasnt even in the back. And i probably didnt even hear him because he falls asleep really easily when you drive the car. And that was it. Reporter he said he didnt realize what hed done until hours later when he got in his car after work and started driving. I caught a glimpse of him in my when i looked to my right to change lanes. Reporter ross said he went flying into the closest parking lot and pulled a lifeless cooper out of his car. A bystander called 911. Theres a baby on the ground. Reporter dash cam video from a Police Cruiser captured ross at the scene minutes later, pacing, hands on his head. I need your i. D. Wheres it at . Reporter it also captured audio of ross exploding in anger at police. Shut the [ bleep ] up. Hold on. All right. All right. All right. All right. You watch your [ bleep ] mouth. Reporter they cuffed him and put him in a patrol car to cool off. And this was the moment when police started wondering about the way ross was behaving. He cried out one moment. Oh, my god. What have i done . Reporter the next moment he seemed calm. Were going to sit here and talk a little bit. Reporter at the police station, detectives who interviewed ross thought his demeanor seemed a bit strange. They noticed hed never shed a tear in front of them. Instead he was casual as they searched his pockets. Im the lead guitar player at Stonebridge Church in the square. Okay, yeah. Reporter even jokey and english is your primary language . It is. Okay. If not, im doing really good. Reporter prosecutor jesse evans. You look at it and say whatever the reaction is that youre supposed to have, that aint it. Reporter but what really got detectives attention was how much ross seemed to know about children dying in hot cars. The worst fear for me is to leave my son in a hot car. And then, just recently, there was a vet on on the internet who said even if youve got your windows rolled down and regardless, you know, im going to show you how hot it can get in the car. The antennas went up on the detectives when they heard that. Reporter detectives werent in the room when ross was finally reunited with leanna, but the cameras rolled. And ross showed a completely different emotion to his wife. You know i didnt mean to. I know you didnt, baby. I know you didnt. I know that. I didnt mean to. I know you didnt. I think my life is over. Its not over, baby. Its not over. Reporter ross pulled himself together and told leanna his story just like hed told the police. I turned out of chickfila, and i just went to work. Like like it was nothing. He wasnt making a sound. You know, i think he fell asleep. For leanna, too. At least i know that hes in heaven right now. I know he is. I know he is. Hes playing with all the trucks in the world. Oh, my boy. Reporter but it was Something Else ross told leanna that really got the investigators attention. I was up and down, dreading he was going to look terrible. He said it while he was talking to leanna that, you know, he was dreading how cooper was going to look when he got him out. Reporter almost like he knew what was there. Exactly. He knew what was going to be found. Reporter they were also struck by how calm leanna seemed to be. And by this surprising question. Did you say too much . Reporter detectives wondered what she meant. They came back into the room and told ross he wasnt going home. Hes going to jail. Hes being charged. Reporter investigators thought they had enough to prove ross had been negligent by leaving his son in the car. His negligence caused the reporter and their investigation was just beginning. Later that night, when katie reached leanna on the phone, she told her shed been sitting outside her home on the sidewalk. And shes told me that, you know, as long as she sat outside, she could pretend like this wasnt happening. Because once she goes inside, you know, theres an empty bedroom where coopers supposed to be. Reporter an empty crib . Theres his toys, his pictures. Its not real if she doesnt go inside. Reporter katie says leanna was numb without her child and her husband. Did she go through that emotion at any point, im angry at you . How could you do this . I dont know that she was ever angry at him. Reporter because you go through that scenario as a parent, what if my spouse did this . Would i be able to understand . But shes such a composed woman. And her faith, i dont think, would let her be angry at him for something that he did not do intentionally. Reporter as coopers family began to grieve, detectives started building their case against ross harris. And what they found convinced them this was no simple case of negligence. They believed this was premeditated murder. 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Freshness for weeks the day after coopers death, ross harris sat in the cobb county jail. His family and friends were in shock. Billy was a pallbearer at coopers funeral. You have to carry that that little casket. You know . Reporter katie says the family grieved in full view of the media. I felt like it was a circus and we were the monkeys. Everybody was watching us. Reporter police were watching, too. Prosecutor susan treadway. We hao there. We have to review all of the evidence. We have to see where it leads us. Reporter investigators pulled Surveillance Video from the chickfila restaurant where ross said he took cooper for breakfast. There they were, father and son. Nothing really seems out of the ordinary. I mean, this looks like a father and son grabbing breakfast. It doesnt look like a child killer waiting to carry out his crime. I would say completely to the contrary. I looked at the video, and when i first saw it and i thought it seemed very out of the ordinary. In particular, the way that he was introducing cooper to some of the workers there. And how they eventually described it to us as being almost like he was putting on a show, almost like he was going out of his way to do that. Reporter but maybe more interesting, prosecutor jesse evans says, was what the video showed about cooper. Coopers wide awake. Didnt appear to be sleepy or anything like that. Reporter ross had told detectives cooper was most likely asleep in the car, and thats why hed forgotten about him. But dkts were skeptica the entire drive from the restaurant to ross office was only about half a mile. And there was Something Else investigators found interesting about ross route that day. Its how quickly he would have forgotten cooper if it happened the way he said. We decided to retrace ross route that day. Were making a right out of the chickfila parking lot and we have to cross a lane of traffic just as ross did to get to this uturn right here. He made this uturn very quickly and then headed toward this intersection up here. And this is a critical intersection coming up. It was here ross had to make a decision. Going left would have taken him to coopers day care. Going straight on would have taken him to work. He went straight on. That means he forgot cooper was in the car within two minutes of strapping him into his car seat and giving him a kiss. It does seem remarkable that we can forget a child in a car very quickly. Reporter dr. David diamond is a neuroscientist at the university of south florida. Hundreds of cases of children who die in hot cars. In a recent case i was involved in in australia, a mother drove one block, a 30second drive, and in a matter of that brief time forgot that her child was in the car. Reporter what were talking about here, there is actually a name for this. This is referred to as forgotten baby syndrome, which actually describes a phenomenon in which normal, attentive and loving parents, for reasons we dont fully understand, lose awareness that their child is in a car. Reporter diamond says it can happen to anyone. Distraction and exhaustion often play a role. He add, once the child is forgotten, the brain plays a dangerous trick. Whats remarkable about these cases is that these parents actually create sort of an artificial memory that the children are actually at day care and that they are safe. Reporter but in this case, investigators were increasingly convinced that coopers death had nothing to do with a slip of the mind. How could you forget something that quickly. Now, i dont know what was going through this mans mind, but i do know that i have five children and i forget things in an instant. It just happens. Is it fair to say, oh, he wouldnt be able to forget something so fast . This is something that if you look at it alone, can somebody forget something that fast . Is it possible . Yes. But then you look at the location of the car seat and all of the other factors together and that showed us that he could not have. Reporter investigators noted that coopers car seat was just inches from the drivers seat. And when they looked at Surveillance Video from ross work parking lot, they saw this, video of ross backing up before he parked. They were sure ross must have seen cooper when he backed up. We wanted to see for ourselves. Were in the same kind of car ross harris was driving. Weve placed the same model of car seat in the same spot cooper was sitting. If i turn around, i can definitely see it. If i use my mirrors to back up, i cant. And there was another detail the Surveillance Video from home depot revealed. Ross had gone to lunch with some friends. There he is getting picked up. But look here, nearly an hour later, there he is again getting dropped off at his car. He opens the drivers door and throws a box of light bulbs onto the front seat. Ross never told detectives about going back to his car in the middle of the day. Did he lie about going to the car or did he just not disclose that he had gone to the car . I think when you look at it in totality, he absolutely lied about it. Reporter investigators were sure ross was hiding something. They believed there was no way he could have opened that door and missed his son in the back seat of the car. Did you consider the possibility that maybe he really did just throw the light bulbs in there and didnt see cooper . Absolutely, but when you look at Ever