police arrive at Tyler Hadley's house, the party is over. Officers see Tyler alone inside, pacing back and forth. And they creep up to this window because they can peek in. Reporter: What kind of... See More
police arrive at Tyler Hadley's house, the party is over. Officers see Tyler alone inside, pacing back and forth. And they creep up to this window because they can peek in. Reporter: What kind of state was he in at that point? They talked about the look on his face, one officer describes it as deranged. Reporter: Officers ask where his parents are -- He said, "They're out of town. They're in west palm beach." He's placed in handcuffs, and the officers go in and search. Reporter: And inside the master bedroom they find what looks more like a garbage pit than a place where Tyler's parents slept just 24 hours before. The room is packed with items from all over the house -- furniture, magazines, pictures, food, mom's "Good housekeeping" magazine, homework from her students, a family calendar. Underneath, investigators find the bodies of Blake and Mary Jo Hadley. It's the darkest turn possible for a Saturday that began with ordinary errands for the hadleys. A trip to the local farmers market, a visit to a dress shop. They were back home early afternoon, his father taking a nap, his mother at the computer. Tyler told his best friend Michael Mandell that to psych himself up he listened to the lil boosie song "Feel lucky." Then he grabbed a hammer. He said that he stood behind his mother for five minutes, while she was on the computer, trying to figure out whether or not he should hit her or not. And at some point, he hit her. Reporter: Mary Jo's screams woke his father. He rushed to the doorway and was stunned by what he saw. And he couldn't even move. And, Tyler said he ran up to his father, hit him, and his father asked him why he's doing this, and he said, "Why the Not." Reporter: Tyler told him that he then dragged his parents' bodies to their bedroom, then spent hours cleaning up the blood. Stripping the walls, leaving empty hooks where family photos once hung, adding them to the pile. At some point, during all of this, Tyler makes that post on Facebook that the party is on. He uses his parents atm card to withdraw $400 in cash and buys beer for the party. At the party he's having a great time. He's playing round after round after round of beer pong. He's laughing, he's joking, he's planning a party for the next night. Reporter: Tom bakkedahl, the prosecutor assigned to the case, tries to make sense of the grisly murders. This is not your kid from the wrong side of the tracks. This is not your kid who was raised in an abusive, violent family. And these parents gave him everything. Reporter: Investigators find evidence that points to premeditation. For months, Tyler repeatedly talked about killing his parents to his friends. His mom took his phone away. And he said he was going to kill her. He said something about, "Oh, I'm just -- I'm going to kill my parents." I just specifically remember him saying I am going to kill my parents. He just said it with a smile, so that's why no one took it too serious. Reporter: But no one knew just how calculating their friend was. He hid his parents' cell phones before killing them, and with no land line, he knew they couldn't call for help. Less than a month before he was to face trial, Tyler pleaded no contest, leaving a controversial question, his punishment. He could be protected by a recent supreme court decision, which ruled that for juveniles life in prison without parole is unconstitutional. But prosecutors argue that with a crime so heinous, Tyler should never see the light of day. He sentenced the whole family to life. Reporter: But Tyler's defense team argues that Tyler was mentally ill. He had major depressive disorder. He was suicidal. Reporter: He was drinking heavily and abusing drugs, but the counter to this would be -- a lot of people have disorders, take drugs. Some even take illegal drugs, yet they don't kill their parents. What I think is one of the most important -- factors, is the juvenile brain. The juvenile brain doesn't fully develop until the age of 25. Reporter: But the prosecutor says Tyler, just 153 days shy of his 18th birthday, should be treated as an adult. As for the motive, could it really just be the party? The prosecutor pored through messages Tyler exchanged with his friends for clues. In that, Tyler complains about the outpatient rehab program he's in writing: "I seriously hate that For real." He wanted to have a party. There's no question about that. The decision over Tyler's fate has ripped the family in two. His mother's side Mary Jo's mother -- Tyler's grandmother, hoping for parole. I just want Tyler not to spend the rest of his life in jail, because I know, I know, I know he's a life worth saving. Reporter: But for his father's family, like Mike and Cindy Hadley, forgiving their nephew is out of the question. This is a cold-blooded murderer that we're talking about here. Yeah, he's my -- he's my nephew and I love him. All right? But there's only one sentence. Is life in prison. Reporter: You don't think there's any way he could rehabilitate himself and be a productive member of society? Would you want him living with you? If he got out? Reporter: Mike's concern, now entirely for Tyler's brother Ryan. That's the person that we need to feel sorry for, he lost his entire family. You know, he lost three people -- his mom and dad and his brother. State your name, please. Ryan Hadley. Do you love your brother still? I do love my brother. Are you hurt for your brother still? Yeah, I hurt for my brother. Reporter: But that love for his baby brother has its bounds. Under what circumstances would you like to maintain this relationship with your brother? Well, what I want is for him to get the maximum penalty possible. Reporter: Finally, Tyler speaks publicly about the crime, but offers little insight as to -- I'd like to direct this to my entire family, everyone, all of them. I know it's hard to understand and you can't begin to explain what happened I just want everyone to know that I am -- I am truly sorry for, you know, the acts I committed. Reporter: The judge was unmoved. Two weeks ago, he made his decision. It is hereby the judgment and sentence of the court, the defendant be sentenced to life without the possibility of parole. No one wants to see a youth behind bars, but he murdered his parents, a colder heart I've never seen. Reporter: If he were here today, if you could speak to him directly right now, what would you say to him? Well, of course, I'd ask the question, why? I might ask him, "Do you miss your mom and dad? Didn't they mean anything to you? Was it worth it? Are you happy now? Hope that party was worth it." You just seen Tyler Hadley's grandmother on the stands saying he has a life worth saving, do you agree? Should he have a chance at parole?
This transcript has been automatically generated and may not be 100% accurate.