I'm Lester Holt. Tonight on Dateland. I heard this loud noise. It sounded like someone was in the house. I opened up her door. I thought, I'm hearing things.

Your instincts were right that something happened in the middle of the night.

You think your child's safe in your home, sleeping? I just had to wake up my daughter for school, and she had a new pulse.

I saw a 16-year-old female laying in her bed. There was a bullet hole in the wall.

So she's been shot?

Someone had fired a shot from outside the residence. She sees a person dressed all in black trying to get in the house, turning the door, beating on the door.

She was shaking.

Oh, my God. This is a real gun.

You're trying to bring down a murder suspect.

I just knew it was something that had to be done.

Everybody comes your hands out of the vehicle now.

It all became a lot more real.

Here's Andrea Canning with Noises in the Night.

When the autumn chill seeps into this community just north of Knoxville, Tennessee, hundreds of high school students are drawn to the blaze of Friday Night lights. To cheer on their home count heroes, the Bobcats. She was the Friday Night Light who perhaps shone brightest of them all. Emma Walker, a Bobcats cheerleader since her freshman year at Central High.

She was a really good cheerleader. Some cheerleaders would just go through the motions. But Emma would put her own sparkle, I guess, into what she would do.

Fellow cheerleaders, Kelsey and Lauren, say their friend Emma could be sassy, too.

She would always say, Well, I am a big deal. And I take it that she said that with a hint of sarcasm? Yes. They're educational snacks of the President. We're going to eat first. People who didn't know her were like, Oh, she's a super pretty cheerleader. Oh, no. But then they would meet her and be like, She's the nicest person I've ever met.

Keegan and Nathan were Emma's longtime school friends.

Once you got to know her, you were like, Wow, she's a down Earth person and really sweet.

She had a smile that could light up the room. A big, beautiful smile.

Emma's parents, Jill and Mark, say that infectious smile was the hallmark of her playful personality.

She liked to play jokes on me by grabbing my iPhone, taking selfies of herself. I had no idea.

Emma volunteered at an animal shelter. At school, she was an honor roll student with a clear career goal.

She wanted to be a neonatal nurse, and when we would talk about the different professions, and we get to the ones about babies, then she was like, That's what I want to do.

It's no surprise that Emma got noticed by boys at school. And there was one boy she definitely noticed back.

That's really all she talked about at first. It was just like, he's super cute.

He was Reilly Gaal, two years older than Emma. Popular, too. A standout wide receiver on the Bobcats football team. Did you ever think Reilly would make it to the NFL?

Yeah, if there was anybody that was going to do it, it definitely would have been Reilly.

Reilly's friends from grade school, Alex and Noah, say he wasn't just a high school jock. He was active at church and loved Star Wars movies.

Started out a nerdy guy. That's how we met, obviously. Obviously. Then a little bit later in the high school, he got a little bit more into football, but he kept with his nerd roots.

He was really funny, and I think that's why Emma fell him in the first place because they were both super goofy. She had a big crush on him. She did.

There was just one problem. Riley already had a girlfriend, but he said he broke up with her to date Emma. Things got serious pretty quickly between the two of them.

Yeah. But as the months went by, it became clear, Riley, the star football player, was also, well, a player.

It turned out his ex wasn't really an ex After all.

He had promised his ex-girlfriend that he would take her to prom that year and take Emma his senior year. She was okay with this? She wasn't okay with it, but she did let it happen. She couldn't let go? No. That must be hard for a parent when you see a guy who's got two girls on the go. That's not cool. No, it's not cool. She was young and had a mind of her own and didn't want us to voice our opinion about our concerns.

Emma's determination to be with Riley caused a lot of tension between her and her parents. How does it work when you're trying to be good parents and your daughter has that strong personality?

It's difficult. Very difficult. I She just was very stubborn and thought her way was the right way. She wanted to learn for herself.

Emma and Riley dated on and off in high school for two years. When Riley graduated and went off to college, just a half an hour away, they tried to keep the relationship going. But just before Thanksgiving, in Riley's freshman year, Emma said she saw Snapchats of Riley with other girls on campus, and she broke up with him for good. Emma's parents say the tension at home evaporated.

It must have felt so good to be the happy family again. It did. The whole household was different.

The household wasn't calm for very long. On November 20th, 2016, a Sunday, Emma went for ice cream with her dad and planned to get up early for school the next morning.

I told her, Good night. Love you. I'm going to bed. And during the middle of the night, I heard this loud noise.

What noise was it?

It sounded like someone was in the house and opened a door and slam it, and then heard it again.

Mark jumped out of bed to check on Emma and her brother.

I opened up her door to her bedroom, and I stared at her for probably 15, 20 seconds, and she was just lying asleep in her bed. I shut the door and went to my son's bedroom, and he was in the bed asleep. So I thought, I'm hearing things. So I checked the doors around the house and went back to bed.

In the morning, Emma's mom, Jill, woke up early.

And wanted to wake her up, and I couldn't wake her up. What's going through your mind in that moment? I had no idea. And I can't recall a lot of it. I just know I checked for a pulse. And there was no pulse? No pulse. So, you know.

Emma's younger brother, Evan, also rushed in.

Poor Evan, too. I'm sure that's something you wish that... I wish he'd never have to experience. It's like a nightmare.

Jill called 911.

I just had to get my daughter for school?

And she had no pulse.

You said that she's non-responsive? Yeah.

What had happened to Emma Walker?

When we come back, the investigation begins. I saw a 16-year-old female laying in her bed with a small amount of blood on her pillow.

People had thought she might have overdosed on something.

They thought that she had ingested poison or whatever.

This is a mystery right now.

It's all a mystery.

Monday, November 21st, 2016, was supposed to be a regular school morning. Instead, first responders were arriving at the Walker family home, and word that something horrible had happened to Emma was tearing through town. Friends calling friends.

She was just bawling. And I was like, Okay, you need to breathe. You need to calm down. What's wrong? And she said, Emma is dead. And I said, What are you talking about? Because it really didn't register in my mind.Not our Emma.Not our Emma.

It didn't seem real at first to Nathan either.

I was like, Yeah, that's my best friend. But no, she didn't pass away. It just hit me. I started bawling.

Emma's ex-boyfriend, Riley, was at his college dorm when phone was flooded with calls and texts. He grieved on social media.

How much he loved her, how much he's going to miss her. She doesn't deserve this. She's in a better place now. Tell God about our Bible verse. Did their hearts go out to Riley, he's lost. A lot of people had commented, I'm so sorry, I'm praying for you.

Still, no one knew yet how Emma died. What are some of the rumors that are now floating around on social media about what happened to Emma.

People had thought she might have overdosed on something. Some people said brain bleed. The biggest one that upset this the most were people who didn't know her were saying that she killed herself. Was there any part of you that was confused and thinking, Well, maybe it's possible? No.

No part of me thought that Emma would ever take her life.

This is a mystery right now as to what happened.

Emma's there, and you know that she has not survived whatever has happened, but you don't know what.

It's all a mystery.

Investigators arrived with just sketchy details from first responders.

They thought that, originally, that it was a suicide, that she had ingested something, poison or whatever.

Knox County Major Mike McClane was assigned to investigate the case with Major Crimes Detective Alan Merritt.

Saw a 16-year-old female laying in her bed with a small amount of blood on her pillow, and some people had confused that with that she had gotten sick or had ingested something and caused her to vomit.

But when the detective looked closer, he saw something unusual. First responders didn't immediately see the hole in the wall. There was a hole in the wall next to Emma's bed, a bullet hole. And while only a little blood was visible on Emma's pillow, when investigators inspected her head, they saw a small entry wound shot. So she's been shot?

Yes, ma'am.

Shot in her own bed.

The bullet struck her just left and above the ear. Basically, was a fatal wound.

She had to have been shot then through the wall?

Yes, it was It was obvious that someone had fired a shot from outside the residence into the residence, striking her in the head.

This is not the neighborhood that has drive-by shootings, right?

Yes, ma'am, that's correct. It's actually a fairly low crime rate area.

As the detectives processed what was now a crime scene, they found more clues as to what might have happened.

We go outside the residence, and that's where we also determined that there was a second shot that had been fired through the end wall of the house.

So, bullet holes in two separate walls, and there in the walker's yard?

We find a shell casing, a spent casing that had been fired. And then as we again work around to the end wall of the residents, we find a spent casing and a live round.

When Emma's parents learned what had happened, they were barely able to take it in.

They had told us that she had been shot.

It's unthinkable. Emma's father, Mark, recalled with horror those noises he'd heard during the night.

Knowing that those noises that I heard were gunshots, and they sounded nothing like gunshots.

But your instincts were that something happened in the middle of the night.

You think your child's safe in your home, sleeping.

But who would want to kill this sweet, popular girl whose goal in life was to care for newborn babies. It turned out the last few days of Emma Walker's life had been anything but normal and might be the key to unraveling the mystery.

Coming up. She sees a person dressed all in black. A mysterious figure at Emma's door. This person starts turning the door knob, beating on the door. She's in fear. She's in a panic.

I have to say I would have been absolutely terrified. Definitely.

When Dateland continues The air hung heavy in the courtroom.

The people pressed shoulder to shoulder. They heard the gossip and the whispers about a family teeming with passion and hate about a mysterious disappearance, and a pile of bones found burning in a lime pit. And now they wanted to know what really happened. But even they were not prepared for the story that came spilling out, the secrets, the lies, the confessions, and the ending so unimaginable. And now you will hear it, too. The Dead Alive: A Morison Mystories. A true story that became a classic novel. Listen now wherever you get your podcasts. Hey, guys. Willy Geist here, reminding you to check out the Sunday Sit Down podcast. On this week's episode, I get together with the busiest man in show business, Ryan Seacrest, to talk about the hustle that has taken him from high school radio DJ to media titan, and of course, his new gig as host of Wheel of Fortune. You can get our conversation now for free wherever you download your podcasts.

How did a master cybercriminal and a Russian oligarch with ties to the Kremlin hack into America's financial system, scamming millions. Cnbc presents The Crimes of Putin's Traitor. Listen wherever you get your podcasts.

Emma Walker was shot dead in her own bed. At 16 years old, she had her whole life ahead of her.

Yeah, all the great things that she would have done. Yeah.

I mean, proms and graduations and things that we never get to see. Getting married, having kids.

As Emma's family began to imagine life without her, police were focused on finding her killer. They were talking to her family and friends about the days right before the shooting. That's a lot of activity in a period of two days. That's unexplained. It was the weekend before Thanksgiving. Friday night, Emma and her group were celebrating a football win at a friend's house. Her friend Zack was at the party when Emma received a text message from an unknown number. The message said something about Riley. He'd been taken. Text messages saying, someone has a Riley.

Someone has a Riley.

Yeah, someone's kidnapped him. Reilly kidnapped? The strange messages kept coming. Then, Emma's phone rang. Reilly was on the line.

Him screaming in the background like, Help me, help me, Emma.

I need your help. You can hear on the call, calling for help? Yes. Emma and her friends rushed out of the house, and there was Reilly.

And he had his hands on his head. He just looked confused. I could see her yelling at him like, What's going on? And she was really angry.

Emma was furious with Riley. She and her friends thought the whole thing was some prank.

We all, as I said, it's very far fetched for him to really be kidnapped. We didn't think twice about it.

But if the kidnapping was joke, what happened the next morning was no laughing matter. Emma's friends told police that Saturday she drove herself home from her friend's house.

As she's pulling in the subdivision, approaching her residence, she sees a person dressed all in black. And as she gets closer, he cinches the hood up and put some sunglasses on.

Emma was texting her friends a play-by-play.

As she gets in the residence, then this person comes to the front door and starts trying to get in the house, turning the door knob, beating on the door. She's in fear. She's in a panic. And so she reaches out to the one person that she thinks can help her, which was Reilly Gaal.

Emma had just broken up with Reilly and was angry at him for what she thought was that strange kidnapping stunt the night before. Still, she texted him this, I hate you, but I need you right now. She FaceTime called him and asked him to come over. Why Why do you think she reached out to him given that they had just broken up?

I think he was a sense of security to her and that he was a protector from other things.

Riley searched the house and neighborhood, but saw no signs of anyone. Neither called the police. But now, detectives were investigating Emma's murder. They discovered surveillance footage from a neighbor's house, and there he was. So this is the mysterious Man in Black? At At that point, it is. Were you able to see a face?

No.

A possible intruder? An attempted kidnapping? What was going on? Police needed to talk to Reilly right away. I'm Detective Maritz. This is Detective Herge. They asked him for details about the kidnapping, and he insisted it really happened.

It was traumatizing. I didn't know what to make of it. Went to my stepdad's house, and I pulled in the driveway, and this van pulled over across in the semicircle. And these two guys were walking across the street. Next thing I know, one of them grabs my back and the other one's around the corner. And they just put their hands over my face and just took me to their van or whatever.

Why would somebody do that to you?

I genuinely have no idea. They did ask me. They were like, Who would you want to talk to for the last time? And so I started freaking out. And I said, Emma. And they made me call Emma. And I was just crying, screaming. She thought it was a joke. She thought I was playing a prank on her.

Emma didn't buy Reilly's kidnapping story, but she was genuinely terrified when she called him the next day about the man in black.

And then when she FaceTime called me, she was crying and freaking out. So I said, okay, give me a minute. I'll come down there and check it out.

That's the only person, Riley could think of who would want to harm Emma.

The only thing that I thought of was whoever the person was at her house Saturday morning. That's the first thing I thought of.

Reilly told police, even though he and Emma were broken up, he still cared for her. In fact, they spoke on the phone Sunday night, in the hours before Emma was shot.

I just told her how much I loved her and that I was sorry that she didn't want what we had anymore. She said she didn't care about the relationship anymore. She said she cared about me. She loved me, but she didn't care to be with me anymore.

Reilly said he spent the rest of that night on campus about 25 miles away, crying over the breakup.

I sat in the parking lot just looking at pictures of us.

He woke up to people texting and calling with their condolences.

So I was like, What are you talking about? Did you not hear what happened? I said, No, what are you talking about?

Reilly, the heartbroken ex. And now he'd lost the love of his life for good. But this pair of seasoned investigators had their radar up.

As you start seeing more of his personality, you can see that he had to have her. Coming up, a closer look at that mysterious man in black. She recognized him by his build, by his gait, the way he walked, the way he carried himself. Who was he?

Emma Walker had been murdered, and all over Twitter, Reilly Gaal was the grieving ex.

Where did he change the bio to? Living every day through Emma Walker. Rest easy, my angel.I love you so much.Yeah..

And now, Emma's friends were looking back on her romance with Reilly, and they remembered a high school boyfriend who was jealous, possessive, even obsessed.

He started to get very He was really controlling of her, where she was, what she did. If she wanted to hang out with our friends, he was like, You're not going.

He didn't want her to hang out with people. It was just him and her.

And if Emma went somewhere without without him.

He would text her 40 to 100 times. He's just blowing her phone up. Emma, Emma, Emma, Emma, talk to me. Talk to me. Text me back. Call me.Yeah.Just over and over again.He'd call her 20, 30 times.

Emma's parents thought the relationship was toxic. They had seen their daughter change. This new personality with Riley in the picture was not one that you recognized?

No, not with Emma.

Her parents said, Riley seemed intent on driving a wedge between Emma and her family.

He would tell her she really didn't have parents, that she really barely had a brother. And I think he just wanted her to think that he was all she had.

Jill and Mark had always been involved loved parents, monitoring their kids' social media and cell phones. They even had a tracker on Emma's car. So when things got bad with Riley, they tried to limit Emma's contact with him, but he always seemed to find a way around their rules.

He would show up to our church because they couldn't tell him to leave or a basketball game because it's a public event going on, so they can't tell him he shouldn't be there.

And when Emma finally broke up with him a few weeks before she died, even his close friend said it seemed like he was unraveling. Were you worried about him?

Yeah, very.

I think this is when we started to see if he wanted to do something like he could. He seemed a little unstable to you? Yeah.

And now that Emma was dead, her friends weren't buying his sad messages on social media.

What are you thinking when you're reading Reilly's posts? He's trying to cover up for himself.

Did you think he did it or something else?

I thought he had something to do with it.

Police were thinking the same thing as they listened to stories about Emma and Reilly.

Based on my experience as a detective, it was an abusive relationship, not physically, but it was more of a psychological on emotional type of abuse.

Police were skeptical of everything Riley said. They didn't believe the kidnapping story. And when they talked to one of Emma's friends in the neighborhood, they were even more suspicious. House. The friend was certain Reilly was the mysterious Man in Black.

She had actually seen the Man in Black and believed it to be Reilly, and she recognized him by his build, by his gait, the way he walked, the way he carried himself.

So during that interview, police were closely watching Reilly. They noted how he referred to Emma in the strangest way.

The girl, she texted me. Which girl? The one that passed away. Okay. What's your name? Emma.

Now, this is someone he's professed his love to and gone on social media and spoke out about how she's his everything and all that. But yet when he goes to talk to me in the interview, he refers to her as the Girl.

How did you get from there? As the interview progressed, police tried to nail down Reilly's whereabouts the night Emma was shot. He stuck to the same story. He was at his college in Maryville, Tennessee. Almost a half hour away, crying in his car over the breakup.

I remember getting back in my dorm at 4:30 in my room and being awake because he asked me why I was getting in so late.

As police questioned Reilly, Is there anybody saw you in your car? They became more and more skeptical, and he was picking up on it.

I hope to God I'm not a suspect in her death. Did I say you were? I hope you don't think it because I wouldn't hurt that girl. I would hurt myself I hurt her, and that's what I've done.

Did you shoot in to him in the house?

No, sir.

Despite his denial, Reilly was now the prime suspect, but they had to let him go. They didn't have enough evidence. And there was a missing piece to the puzzle. Where was the gun that killed Emma? It would take two young men on a dangerous mission to find it.

Coming up.

I'm trusting you guys with my life.

Hidden and a secret operation.

They set up a listening device in the car.

And the police could hear you, but you couldn't hear them. Yeah. Say.

Could these two friends find that missing gun and the killer?

This potentially could be very dangerous. Absolutely.

When Dateline continues.

For true crime fans, nothing is more chilling than watching Dateline. Have you ever seen such a thing before? For podcast fans, nothing is more chilling than listening. What goes through your mind when you make a discovery like that? And when you subscribe to Dateline Premium, it gets even better.

Excuse me, I sound a little skeptical.

Every episode is ad-free. Oh, wow. So this could be your ace in the hole. And not just ad-free, you also get early access to new intriguing mysteries and exclusive bonus content. So what were you afraid of? Dateline Premium. Subscribe now on Apple Podcasts, Spotify, or datelinepremium. Com.

You ready for what's coming?

The day before Emma Walker was killed, Reilly Gaal's grandfather called police about a handgun he owned.

He files a report that the gun stolen.

That missing gun was a problem for Reilly, too. He lived with his grandpa, and the gun was the same caliber as the one used to kill Emma. Police didn't think that was a coincidence. Did he express that he knew where the gun was, or did he completely deny? He completely denied everything relevant to the gun. And after his denials to police, Riley reached out to his close friends, Alex and Noah. Since his breakup with Emma, Riley had been leaning on them for support. What did he say about how he felt about it?

He was just torn up. Throughout this whole time, I tried to spend as much time with him as I could, just be there for him whenever he needed.

Riley confided in Alex and Noah again. He said he would never hurt Emma. Had nothing to do with the shooting, but he did have his grandpa's gun.

They're going to find a way to put this on me if they find the gun. It's like, Can you just help me get rid of this?

The boys were willing to comfort Riley, but not help get evidence in a murder investigation. Instead, they called Lieutenant Merritt.

It's amazing that they called.

Oh, absolutely.

I mean, this is a big piece of the puzzle.

Absolutely. They could very well just went on living their lives minding their business.

Reilly told his friends he planned to go to the bluffs high above the Tennessee River and toss the gun into the water. Police hatched a plan, a bold and risky sting operation. Have Alex and Noah go with Reilly and the moment they see the gun, signal detectives who would swoop in and make an arrest. This potentially could be very dangerous.

Absolutely. You're going to have two boys in a car with a guy that's believed to have already killed one person with a murder weapon. This is a huge dangerous thing.

Dangerous? For sure. And then, detectives made it even more complicated. They decided to secretly record the whole thing.

They set up a listening device in the car itself. My car had a little one inside the color of my jacket, which sucked because I couldn't take off my jacket the whole time. And then you got the key fob that took the video as well.

And the police could hear you, but you couldn't hear them.

Yeah.

Everything came together with lightning speed. Just hours after calling police, 18-year-olds Alex and Noah were wired up and ready to meet Riley. What did your parents think about this? They're very vulnerable in this position.

My parents had just moved to North Carolina. I was living in Tennessee on my own. I didn't have time to talk to my dad about it.

You did not tell your parents.

I didn't.

The plan hinged on the boys texting a secret word to detectives the moment they see the gun. Without tipping off Riley, the pressure was intense. Oh, man. This is insane. Riley came over to Noah's house. The mission was underway.

I know that she was in love and cared about me a lot. We spent two years together.

Police were nearby listening in. As instructed, the boys tried to be natural.

I'm sorry about your met dog. I can't. I really... I want to be so upset, and I can't because I'm no more about getting arrested and putting away for murder that I didn't commit. Never in my life would I kill someone that I love that much. Love you, bro. It sucks you got to deal with all this, man.

Reilly clearly had no a clue about the sting. He had faith in his friends.

I'm trusting you guys with my life because this is 70 years in jail. If I get convicted of something I didn't do. Why can't you just give him a gun? It just needs to be gone. For whatever reason. It just needs to be gone. You guys don't have to come with me if you don't want to. I got your bag, man. If it's in the Tennessee River, they will never find it.

The boys headed out. First stop to the back of the house, where he'd hidden the gun. He came out holding a plastic garbage bag. Detectives were still tracking the boys closely or trying to.

It's a crazy part here. We've got detectives watching them. They leave out from stepdads, and at some point, we lose them. We lose sight of the vehicle. We've lost the wire.

Is that a heart beating moment?

Yes. Obviously, we want to track them real-time. We want to keep up with Police did find them again in time to see the boys make an odd detour.

On their way to the river, they stop for some drive-through fast food.

Yeah, I need a Cajun chicken with two sides of hush puppies with chili and cheese on it and a large dog's hot pepper. Have you tried the good cat sauce? No. Huh? No. Oh, my God. Try it.

You're in the middle of this critical undercover operation, and you've decided go for chili cheese fries?

Yeah. Why?

It was almost the whole time we were saying goodbye to one of our best friends. It was almost just comforting to have it be like it was before.

They got to the bluffs around 11:00 and pulled into an apartment complex parking lot. Alex knew the security code for the gate. He used to make deliveries there. And then the big moment. The hidden camera didn't catch it, But Alex and Noah will never forget it. Riley pulled the gun out of the bag.

Oh, my God.

Noah texted the detectives. They were supposed to pounce, but 30 seconds passed. Then a minute. No police. Alex saw their SUVs outside the gate. What was the delay? Two minutes. Still no police. The tension was unbearable. Then Alex did something audacious. He took the gun out of Reilly's hand. This is a real gun. Alex, why did you take the gun from Reilly? That was a bold middle.

Yeah, it really was. I was watching from the back seat. It was just like an instinctual thing, and Reilly grabs it back out of my hands. That was scary.

And that was when police got through the gate and made their move. What the fuck? What the fuck? Everybody, put your hands out of the vehicle now. Reilly was cuffed and taken away. The gun was still in the car.

Just pull that bag enough just to see the serial number.

The mission was a success. Alex and Noah were safe. Reilly was charged with the murder of Emma Walker and taken to jail. It was the end of a long, crazy day. A popular football hero was behind bars. How did it all come to this?

He was controlling and obsessive, but you never thought like a murderer.

And in a case already full of surprises, the biggest one was still to come.

Coming up, a sudden change in Reilly's story. And And it's a stunner. He was holding that he could come to a rescue.

What Reilly is saying is, I'm not a cold-blooded killer.

Would the jury believe it?

Almost a year and a half had passed since Emma Walker was shot and killed through the wall of her bedroom. Emma's ex, Reilly Gaal, pleaded not guilty to first-degree murder. Knox County district Attorney General, Sharm Allen, prepared for a high-profile trial. Why do you think this case has captured so much attention?

People People can relate to being a teenage couple in love. People can relate to breakups.

I think one thing that really scared people in our community was that Emma was asleep in her own home, in her own bed.

Was it stressful as the trial approached? Yes.

Very.

Just the worries of what the turnout will be.

Prosecutors Kevin Allen and Molly Martin would have to prove to a jury that it was Reilly who pulled the trigger her. What was your strategy going into this trial?

I think the main thing we needed to focus on in the beginning was putting him there that night. And so I think the cell phone records and the GPS locations were very important. Up until that moment. They placed him around Emma's house? He placed himself in Marible, and the phone records placed him back in Knoxville. So he had clearly told a lie about where he was? Yes.

But on the first day of trial, Reilly's defense attorney, Wesley Stone, upended the state's case with an unexpected admission. Reilly was there, did fire the gun, but it was not murder.

That was a fairly stunning client.

From the gallery, veteran crime reporter Jamie Satterfield saw Jaws drop.

What he said was that Reilly never intended to kill her, and in fact, assumed he would not kill her if he shot through a wall. We'll ask you to find Mr..

Gaal guilty of reckless homicide.Not premeditated murder.Right..

In Tennessee, that's two to four years in the penitentiary.

That would be a huge difference. Yeah. All of the state's preparation went out the window. The case went from a who done it to a state of mind defense. The defense said Reilly wasn't some crazy killer, just crazy in love with Emma, with a bizarre plan to win her back.

When Reilly Gaal fired that shot in the backyard, as crazy as it is and as bizarre as it is, he was hoping that he could come to a rescue.

The defense told the jury Reilly only meant to scare Emma with the gunshots. Then, with Emma needing comfort, he'd swoop in and be her night in shining armor. His attorney argued, Reilly had no idea that those bullets would pass through the house. Some of us who know about firearms may very well know that if you shoot into a house, it'll go through the wall. Some of us may not.

And I submit to you, Reilly Gaal, did not.

The defense denied Reilly was the man in black, but admitted that the kidnapping story was a ruse, a stunt to get Emma's attention. Reilly's attorney said it showed how desperate his client was to be with her. What Reilly was trying to do is get an opportunity to see him.

And that would It had later become a theme of his defense that rather than killing Emma, what he intended to do was play her rescuer. It almost does sound like he was just trying to scare her when you first hear it. I would think the same thing. And then I went out to the scene and looked at the house and looked at where he would be standing. And it is, what, 5 feet away from the house, I think the measurements were. And it's me pointing a gun right at you right now and pulling the trigger. It was that close.

So close, prosecutors said. It was obvious that Reilly was shooting to kill.

Shoot up into the air, shooting through the window, anywhere. But where are you shot?

The state agreed with the defense on one point. Reilly was desperate to be with Emma, but that desperation had become dangerous. Prosecutors argued, of course, he was the man in black. After that, and the kidnapping stunt failed, they said Reilly gave up on winning her back. Instead, he peaked into Emma's backyard, stood outside her window, and fired into the wall, knowing exactly where she slept on the other side.

I think this is a case about revenge. I think that he sought to get back at her for the hurt that he perceived that she was purposely putting on him by breaking up with him.

And after he killed her, the prosecutor said he went to great lengths to cover his tracks. And he is going to throw the gun off the block? Yes, sir. Okay. They showed the jury the video of that undercover sting and how Reilly tried to manipulate his closest friends into covering up his crime.

I'm trusting you guys, like with my life.

His plan was to get away with this.

His plan was never to be caught. Which theory would the jury believe? A reckless act or premeditated murder? They went off to deliberate and came back four hours later. In count one, charging the defendant with first-duty murder. Did the jury reach a verdict?

Yes, we did.

What did you agree?

Guilty.

You hear guilty?

What's that moment like? Relieved?

That's a sense of relief.

Reilly was sentenced to life in prison. He'll be in his 70s by the time he's eligible for parole. We're incredibly proud of all the investigators and all the work, but we're almost more proud of Noah and Alex.

I mean, are they the heroes in this?I.

Think they really are.Yeah, I really do. Lieutenant Merritt, the Walkers, they call you the heroes. What do you say to that?

Just did what I had to do.

It took a lot of guts to do what you did.

I appreciate that.

As For Emma, who used to joke that she was a big deal, she's actually become one with tributes to her all over town. There's a scholarship in her name at Central High, and a dog park dedicated to the young animal lover.

It's just a great It's a fun, happy place to come and remember her and for other people to remember her.

Here at the East Tennessee Children's Hospital, a NICU exam room has been named in her memory. But Emma's parents believe the best way to honor their daughter is to learn from what happened. Detective Merritt says it is important to understand when teenage drama turns into dangerous behavior.

I think we need to educate our young people better about relationships and what a healthy relationship is and what is psychological abuse, emotional abuse. That's what we hope someone gets out of the story is, awareness.

And know what's healthy for you.

Emma may be gone, but for those who loved her, the young girl still sparkles.

She'd want to be out there, and she'd want us to be laughing and having fun and not... You can't cry all day. You have to live life.

That's all for now. I'm Lester Holt. Thanks for joining us.