going to ask him to write one sentence about my mother to me every week while he's in prison so he has to think about her and i can remember her again. >> that's all for this edition of "dateline." i'm craig melvin. thank you for watching. of dateline. i'm craig melvin. thank you for watching. i'm craig melvin. >> and i'm natalie morales. >> and this is "dateline." during the middle of the night i heard this loud noise. it sounded like someone was in the house. i opened up her door to her bedroom and i thought, "i'm hearing things.” >> your instincts were right. something happened in the middle of the night. >> you think your child's safe in your home, sleeping. >> she was just 16. emma, the honor student. cheerleader. volunteer. >> she could get along with

anybody. >> always so like, kind hearted and sweet. >> she wanted to be a nurse. she had a plan. >> she went to sleep one sunday night and never woke up. >> 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. >> was emma a target? that weekend she'd seen a mysterious figure dressed in black. >> turning the doorknob, beating on the door. she was in fear. she was in a panic. >> she was shaking. >> now, two brave friends set out on a secret mission. could they help catch her killer? >> you're trying to bring down a murder suspect. >> i just knew it was something that had to be done. >> this is insane! >> everybody put your hands outta the vehicle now! >> it all became a lot more real. hello and welcome to

dateline. ema walker was a spirited teenager with a knack for stirring up fun. pretty and smart she had a whole life ahead of her. but after her death detectives faced a tough investigation. whoever shot emma had been brazen, and it would take a brave plan to catch her killer. here's andrea canning with "noises in the night.” >> reporter: 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 hometown 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 kind of go through the motions

but emma would put her own kind of sparkle, i guess, into what she would do. >> reporter: fellow cheerleaders kelsey and lauren say their friend emma could be sassy too. >> she would always say, "well, i am kind of a big deal.” >> reporter: and i take it that she said that with a hint of sarcasm? >> yes. >> they're educational snacks of the presidents. >> who you gonna eat first? >> people who didn't know her were, like, "oh, she's, like, the super pretty cheerleader," like, "oh, no.” but then they would meet her and be, like, "she's the nicest person i've ever met.” >> reporter: keegan and nathan were emma's longtime school friends. >> once you got to know her, you were, like, wow, like, she's, like, a down to earth person. and, like, really sweet. >> she had a smile that could light up the room. a big, beautiful smile. >> reporter: 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 grabbin' my iphone, takin' selfies of herself. and i'd had no idea, but --

>> reporter: 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, like, the different professions, and we'd get to the ones about babies, then she was, like, "that's what i wanna do.” >> reporter: 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, like, talked about at first, was just, like, "he's super cute.” >> reporter: he was riley gaul. two years older than emma. popular too. a standout wide receiver on the bobcats football team. >> reporter: did you ever think riley would make it to the nfl? >> if there was anybody that was gonna do it, it definitely would have been riley. >> reporter: and riley'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. >> he started out kind of a nerdy guy. that's -- that's how we met, obviously. >> reporter: obviously.

>> and then, a little bit later into 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 for him in the first place. 'cause they were both super goofy. >> reporter: she had a big crush on him. >> uh-huh. she did. >> reporter: there was just one problem. riley already had a girlfriend. but he said he broke up with her to date emma. >> reporter: and things got serious pretty quickly between the two of them. >> yeah. >> yeah. >> reporter: 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, like, promised his ex-girlfriend that he would take her to prom that year. and take emma his senior year. >> reporter: she was okay with this? >> she wasn't okay with it. but she did let it happen. >> reporter: she couldn't let go? >> no. >> reporter: that must be hard for a parent when you see a guy who has got two girls on the go. that's not cool. >> no, it's not cool. and she was young and -- and had

a mind of her own, and didn't want us to voice our opinion about our concerns. >> reporter: emma's determination to be with riley caused a lot of tension between her and her parents. >> reporter: 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 mean she just was very stubborn and thought her way was the right way. she wanted to learn for herself. >> reporter: 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. >> reporter: it must have felt so good to be the happy family again. >> it did. the whole household was different. >> reporter: 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 "goodnight. love you. i'm going to bed.” and during the middle of the night i heard this loud noise. >> reporter: what kinda noise was it? >> it sounded like someone was in the house and opened a door and slammed it. and then i heard it again. >> reporter: 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. and 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. >> reporter: in the morning, emma's mom jill woke up early.

>> i went in to wake her up. and i couldn't wake her up. >> reporter: 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. >> reporter: and there was no pulse? >> no pulse. so, you know -- >> reporter: emma's younger brother evan also rushed in. >> reporter: poor evan, too. i'm sure that's something you wish that -- >> i wish he'd never have to experience. it's like a -- a nightmare. >> reporter: jill called 911. >> i just tried to wake up my daughter for school and she has no pulse. >> you said that she's non-responsive? >> yeah. >> reporter: what had happened to emma walker? >> coming up -- 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 that she might have overdosed on something.

>> they thought that she had ingested poison or whatever. >> reporter: this is a mystery right now. >> it's all a mystery. >> when "dateline" continues. ws ♪let's make lots of money♪ ♪you've got the brawn♪ ♪i've got the brains♪ ♪let's make lots of♪ ♪uh uh uh♪ ♪oohhh there's a lot of opportunities♪ with allstate, drivers who switched saved over $700. saving is easy when you're in good hands. allstate click or call to switch today. your mission: stand up to moderate to severe rheumatoid arthritis. and take. it. on... ...with rinvoq. rinvoq a once-daily pill can dramatically improve symptoms... rinvoq helps tame pain, stiffness, swelling. and for some rinvoq can even significantly reduce ra fatigue. that's rinvoq relief. with ra, your overactive immune system

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ask your prescriber or an online prescriber if cologuard is right for you. i'll do it. good plan. >> reporter: 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 and you need to calm down. what's wrong? and she said, emma is dead, and i said, what are you talking about? cause it really didn't register in my mind. like -- >> not our emma. yeah. >> not our emma, no. >> reporter: it didn't seem real at first to nathan either. >> and i was, like, yeah, that's my best friend, but no, she didn't pass away. it just hit me and, like, i started bawling. >> reporter: emma's ex-boyfriend riley was at his college dorm when his phone was flooded with calls and texts. he grieved on social media. >> you know, how much he loved her, how much he's going to miss her. like 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? the -- you know, he's lost -- >> a lot of people -- >> had commented, i'm so sorry. >> prayers for you. >> reporter: 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 us the most were people who didn't know her were like, saying that she killed herself. >> was there any part of you that was confused and thinking, well, maybe it's possible? >> no. >> like, no part of me thought that emma would ever take her life. >> this is a mystery right now as to what happened. >> uh-huh. >> emma's there, and you know that she's -- has not survived whatever has happened, but you don't know what. >> no. >> it's all a mystery. >> reporter: 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. >> reporter: knox county major mike maclean was assigned to investigate the case with major crimes detective allen merritt. >> i 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 -- or, you know, had ingested something and caused her to vomit. >> reporter: but when the detective looked closer, he saw something unusual. >> first responders didn't immediately see the hole in the wall. >> reporter: there was 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. >> so she's been shot? >> yes, ma'am. >> reporter: shot in her own bed. >> the bullet struck her just left and above the ear. it basically was a fatal wound. >> she had to have been shot, then, through the wall? >> yes. it was kind of obvious that someone had fired a shot from outside the residence into the residence striking her in the head. >> this is not the kind of neighborhood that has drive-by

shootings. right? >> yes, ma'am. that's correct. it's actually a fairly low crime rate area. >> reporter: 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. >> reporter: so bullet holes in two separate walls, and there in the walkers' 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 residence, we find a spent casing and a live round. >> reporter: 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. >> uh-huh. >> 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 right, that something happened in the middle of the night. >> uh-huh. >> you think your child is safe at your home sleeping. >> reporter: 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. >> reporter: a mysterious figure at emma's door. >> and then this person comes to the front door and starts trying to get in the house. turning the doorknob, beating on the door. she's in fear. she was in a panic. >> i have to say, i would have been absolutely terrified. >> definitely. >> reporter: when dateline continues. line continues.

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>> reporter: emma walker was shot dead in her own bed. at 16 years old, she had her whole life ahead of her. >> all the great things that she would've done. >> yeah. i mean, proms and graduations and things that we never get to see, you know? getting married, having kids. >> reporter: 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. >> it's a lot of activity in a period of two days that's unexplained. >> reporter: it was the weekend before thanksgiving. friday night, emma and her group were celebrating a football win at a friend's house. her friend zach 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, sayin' like, "someone has riley.” >> reporter: someone has riley? >> yeah. >> someone's, like, kidnapped him. >> reporter: riley, kidnapped? the strange messages kept coming. then, emma's phone rang. riley was on the line. >> him screamin' in the background, like, "help me. help me, emma!” like, "i need your help.” >> reporter: you can hear riley on the call? calling for help? >> yes. >> reporter: emma and her friends rushed out of the house and there was riley.

>> and he had his hands on his head. he just looked confused. i could see her, like, yelling at him like, "what's going on?” and she was really angry. >> reporter: emma was furious with riley. she and her friends thought the whole thing was some kind of prank. >> we all kinda -- as i say, like, "ehhh. it's very far-fetched for him to really be kidnapped.” we didn't think twice about it. >> reporter: but if the kidnapping was a 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, you know, he -- he cinches his hood up and puts some sunglasses on. >> reporter: 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, you know, trying to get in the house, turning the doorknob, beating on the door. she's in fear. she's in a panic. and so, she reaches out to the one person that -- that she thinks can help her which was riley gaul. >> reporter: emma had just broken up with riley 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 do you think he reached out to him given what -- that they had just broken up? >> i think he was sense of, like security to her. and that, you know, he was a protector from other things. >> reporter: 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 that point, it is. >> reporter: were you able to see a face? >> no. >> reporter: a possible intruder. an attempted kidnapping. what was going on? police needed to talk to riley right away. >> i'm detective merritt. >> reporter: 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. i went up to my step-dad's house. and i pulled in the driveway. and this van pulled over across from the semicircle. and these two guys were, like, walkin' across the street. the next thing i know, one of 'em grabs my back, and the other one's around the corner. and they just, like, put their hands over my face and just took me to their van or whatever. >> i mean, why would somebody do that to you? >> i -- i genuinely have no idea. they did ask me, they were, like, you know, like, "oh, who would you want to talk to for the last time?” and i started freakin' out. and i said, "emma.” and they made me call emma. and i was just cryin', screamin', she thought it was a joke. she thought i was playin' a prank on her. >> reporter: emma didn't buy riley's kidnapping story. but she was genuinely terrified when she called him the next day about the man in black.

>> that was when she facetime called me. and she was cryin' and freakin' out, and so i said, "okay, give me a minute. i'll come down there and check it out.” >> reporter: 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 on saturday morning that's the first thing i thought of. >> reporter: riley 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. >> reporter: riley said he spent the rest of that night on campus about 25 miles away crying over the break-up. >> i sat in the parking lot just looking at pictures of us. >> reporter: he woke up to people texting and calling with

their condolences. >> so, i was like, "what are you talkin' about?” and "did you not hear what happened?” i said, "no. what are you talkin' about?” >> reporter: riley, 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 could see that he had to have her. >> reporter: coming up -- a closer look at that mysterious man in black. >> she had actually seen the man in black. she recognized him by his build, hisigate, the way he walked and carried himself. >> who was he? when dateline continues. was he? when dateline continues. with less eczema, you can show more skin. so roll up those sleeves. and help heal your skin from within with dupixent. dupixent is the first treatment of its kind that continuously treats moderate-to-severe eczema, or atopic dermatitis, even between flare ups. dupixent is a biologic, and not a cream or steroid. many people taking dupixent saw clear or almost clear skin,

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i'm dara brown. here's what's happeningch a volcano erupted in iceland for the first time in nearly 6,000 years. it occurred not far from the capital. iceland's prime minister asked people to stay away from the area but said there wasn't a threat to any towns. and the tokyo olympics won't let in spectators coming from outside japan. the international olympic committee said the restrictions are due to coronavirus concerns.

the games will take place between late july and early august. now back to "dateline." welcome back to dateline. i'm natalie morales. who shot emma walker? the day before she died a menacing man dressed in black showed up at her house triggering a panicked call to her ex-boyfriend riley gaul. now detectives were about to discover something riley didn't tell them, and it would send the investigation into overdrive. once again here's andrea canning with "noises in the night." >> reporter: emma walker had been murdered. and all over twitter riley gaul was the grieving ex. >> reporter: what did he change the bio to? >> living every day through emma walker. >> rest easy, my angel. i love you so much. >> yeah. >> reporter: and now emma's

friends were looking back on her romance with riley. and they remembered a high school boyfriend who was jealous, possessive, even obsessed. >> he started to get very kind of controlling of her, like, where she was, what she did, like, 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, like, it was just him 'n' her. >> reporter: and if emma went somewhere without him -- >> he would text her 40 to 100 times. >> and he's just blowing her phone up. >> yeah, seeing -- >> emma, emma, emma, talk to me. talk to me. text me back. call me. >> yeah. >> just over and over again. >> and he'd call 20, 30 times. >> reporter: emma's parents thought the relationship was toxic. they had seen their daughter change. >> reporter: this new personality with riley in the picture was not one that you recognized? >> no. not with emma. her fun loving sell was very

closed off, more in her room. >> was it kind of like her spark had been extinguished? >> yes. >> reporter: 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 that was -- he was all she had. >> this is nightmare situation for a parent. >> cres. >> reporter: jill and mark had always been involved 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 couldn't tell him he shouldn't be there. >> reporter: and when emma finally broke up with him a few weeks before she died, even his close friends said it seemed

like he was unraveling. >> reporter: were you worried about him? >> yeah, very. very. >> i think this is when we started to see, like, if he wanted to do something, like, he could. >> reporter: he seemed a little unstable to you? >> yeah. >> reporter: and now that emma was dead her friends weren't buying his sad messages on social media. >> reporter: what are you thinking when you're reading riley's posts? >> he's trying to cover up for himself. >> reporter: did you think he did it, or something else? >> i thought he had something to do with it. >> reporter: police were thinking the same thing as they listened to stories about emma and riley. >> based on my experience as a detective it was an abusive relationship not physically. but it was more of a psychological and emotional type of -- of abuse. >> reporter: 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. the friend was certain riley was the mysterious man in black. >> she had actually seen the man in black and believed it to be riley. she recognized him by his build, by his gait, the way he walked, the way he carried himself. >> reporter: so during that interview police were closely watching riley. they noted how he referred to emma in the strangest way. >> the girl, she -- she texted me. >> which girl? >> the one that passed away. >> oh, okay. what -- what's her 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.” >> reporter: as the interview progressed police tried to nail down riley'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 break-up.

>> i remember gettin' back in my dorm at 4:30, and my roommate bein' awake, 'cause he asked me why i was gettin' in so late. >> reporter: as police questioned riley -- >> is there anybody saw you in your car? >> reporter: 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 -- >> in my experience it was over the top, it was phony. >> i would hurt myself before i'd hurt her, and that's what i've done. >> did you shoot into emma's house? >> no, sir. >> reporter: despite his denial riley 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. >> riley gaul is about to become the target of a secret

operation. coming up -- >> they setup a listening device in the car. >> and the police could hear you but you couldn't hear them. >> could these two friends find the missing gun and the killer? this potentially could be very dangerous. >> absolutely. you're going to have two boys in a car with a guy believed to have already killed one person with a murder weapon and this is a huge, dangerous thing. >> when dateline continues. s th. >> when dateline continues ♪ it's irresistibly delicious.♪ ♪ more almond breeze, please! ♪ you could take your ulcerative colitis treatment in a different direction. talk to your doctor about xeljanz, a pill, not an injection or infusion, for adults with moderate to severe ulcerative colitis when a certain medicine did not help enough. xeljanz is the first and only fda-approved pill for moderate to severe uc. it can reduce symptoms in as early as two weeks, improve the appearance of the intestinal lining, and provide lasting steroid-free remission.

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>> reporter: the day before emma

walker was killed, riley gaul's grandfather called police about a handgun he owned. >> he files a report that the gun's stolen. >> reporter: that missing gun was a problem for riley 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 -- >> yeah. he completely denied everything relevant to the gun. >> reporter: 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. >> reporter: 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, whatever he needed. >> reporter: 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 gonna find a way to put this on me if they find the gun. like, can you just help me get rid of this? >> reporter: the boys were willing to comfort riley but not help get rid of evidence in a murder investigation. instead, they called lieutenant merritt. it's amazing that they called. >> oh, absolutely. >> reporter: i mean, this -- >> they -- the -- >> reporter: this is a big piece of the puzzle here. >> absolutely. absolutely. they could've very well just went on living their lives minding their business. >> reporter: riley 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 riley 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 gonna have two boys in a car with a guy that's believed to have already killed one person with the murder weapon. you know, this is a huge, dangerous thing. >> reporter: 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. i had a little one inside the cut 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. >> reporter: and the police could hear you, but you couldn't hear them? >> uh-huh. >> yeah. >> reporter: 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? you're very vulnerable in this position. >> yeah. >> listen, my -- my parents had just moved to north carolina. i was living in tennessee on my own. and i didn't have time to talk to my -- >> reporter: you did not tell your parents? >> i didn't. >> reporter: 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. >> holy [ bleep ], man. this is insane. >> reporter: riley came over to noah's house. the mission was under way. >> i know that she really loved me and cared about me a lot. we spent two years together. >> reporter: police were nearby listening in. as instructed, the boys tried to be natural. >> i'm sorry about emma, dog. >> i can't -- i really -- i want to be so upset. and i can't. because i'm worried 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 gotta deal with all this, man. >> reporter: riley clearly had no clue about the sting. he had faith in his friends. >> i'm trustin' you guys, like, with my life. 'cause, i mean, this is 70 years in jail if i get convicted of something i didn't do. >> why can't you just give 'em the gun? >> just -- it just needs to be gone.

for whatever reason, just -- it just needs to be gone. you guys don't have to come with me if you don't want to. >> i mean, i got your back, man. >> if it's in the tennessee river, they will never find it. >> reporter: the boys headed out. first stop, riley's stepfather's 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. >> this is kind of a crazy part here. we -- we've got detectives watching them. they leave out from step dad's. and at some point, we lose them. i mean, we -- we -- we lose sight of the vehicle. we've lost the wire. >> reporter: is that a heart beating moment? >> yes. obviously, we wanna track them real time. we wanna keep up with them. >> reporter: police did find them again in time to see the boys make an odd detour. on their way to the river, they stopped for some drive-thru fast food. >> uh yeah, i need a cajun chicken with two sides of hush puppies with chili and cheese on

it and a large dr. pepper. >> have you tried the cookout sauce? >> huh? >> no. >> oh, my god. try it. >> reporter: you're in the middle of this critical undercover operation and you decide to go for chili cheese fries? >> yeah. >> reporter: why? >> it was like almost the whole time we were, like, saying goodbye to one of our best friends. like it was like -- almost just like comforting to, like, kinda -- have it be like it was before. >> reporter: 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. >> reporter: 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 riley's hand. >> this is a real gun. >> reporter: alex, why did you take the gun from riley? that was kind of a bold move. >> yeah, it really was. i mean -- >> i was watchin' from the back seat. i was like, "dude, no!” >> it was just kind of like an instinctual thing, and riley grabs it back out of my hands. >> yeah. >> that was scary. >> reporter: and that was when police got through the gate and made their move. >> what the [ bleep ]? >> let me see your hands. >> what the [ bleep ]? >> everybody put your hands outta the vehicle now. >> reporter: riley was cuffed and taken away. the gun was still in the car. >> just pull that back enough and let's -- just to see the serial number. >> reporter: the mission was a success. alex and noah were safe.

riley 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'd never thought, like, a murderer. >> reporter: and in a case already full of surprises, the biggest one was still to come. >> reporter: coming up, a sudden change in riley's story, and it's a stunner! >> as crazy as it is and as bizarre as it is, he was hoping that he could come to her rescue. >> what riley is saying is i'm not a cold-blooded killer. >> reporter: would the jury believe it? >> in count one charging the defendant with first degree murder did the jury reach a verdict? >> when dateline continues. y re verdict? >> when dateline continues [ chuckles ] don't get me wrong, i love my rv, but insuring it is such a hassle.

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>> reporter: almost a year and a half had passed since emma walker was shot and killed through the wall of her bedroom. emma's ex, riley gaul, pleaded not guilty to first degree murder. knox county district attorney general charme allen prepared for a high profile trial. >> reporter: why do you think this case has captured so much attention? >> people can relate to being a teenage couple in love. people can relate to break-ups. and i think one thing that really scared people in our

community was that emma was asleep in her own home in her own bed. >> reporter: was it stressful as the trial approached? >> yes. >> very. >> just the worries of what the turnout will be. >> reporter: prosecutors kevin allen and molly martin would have to prove to a jury that it was riley who pulled the trigger. >> reporter: 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. >> reporter: they placed him around emma's house. >> he placed himself in maryville. and the phone records placed him back in knoxville. >> reporter: okay. so he had clearly told a lie about where he was? >> yes. >> the picture that we painted of riley gaul was a deceiver. somebody that was phony that -- i mean, you couldn't get the truth out of him if you tried.

>> reporter: but on the first day of trial, riley's defense attorney wesley stone up-ended the state's case with an unexpected admission. riley was there, did fire the gun, but it was not murder. >> that was a fairly stunning claim. >> reporter: from the gallery, veteran crime reporter jamie satterfield saw jaws drop. >> what he said was that riley 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. gaul guilty of reckless homicide. >> reporter: not premeditated murder? >> right. >> in tennessee, that's two to four years in the -- >> reporter: wow. >> penitentiary. >> reporter: that would be a huge difference -- >> yeah. >> reporter: all of the states' preparation went out the window. >> the case went from a whodunit to a state of mind defense. >> reporter: the defense said riley wasn't some crazy killer, just crazy in love with emma. with a bizarre plan to win her

back. >> when riley gaul fired that shot in the backyard, as crazy as it is, and as bizarre as it is, he was hopin' that he could come to her rescue. >> reporter: the defense told the jury riley only meant to scare emma with the gunshots. then, with emma needing comfort, he'd swoop in and be her knight in shining armor. his attorney argued riley had no idea that those bullets would pass through the house. >> some of us that 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, riley gaul did not. >> reporter: the defense denied riley was the man in black, but admitted that the kidnapping story was a ruse. a stunt to get emma's attention. riley's attorney said it showed how desperate his client was to be with her. >> what riley was trying to do

is get an opportunity to see emma. that's what he was trying to do. >> and that would later become a theme of his defense, that rather than killing emma, what he intended to do was play her rescuer. >> reporter: 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, five 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's that -- it was that close. >> reporter: so close, prosecutors said it was obvious that riley was shooting to kill. >> shoot up into the air. shoot into -- shoot in through the window. anywhere but where you shot. >> reporter: the state agreed with the defense on one point. riley 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 riley gave up on winning her back. instead, he sneaked 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 -- 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. >> reporter: and after he killed her, the prosecutors said he went to great lengths to cover his tracks. >> and he is going to throw the gun off the bluff? >> yes, sir. >> ok. >> reporter: they showed the jury the video of that undercover sting and how riley tried to manipulate his closest friends into covering up his crime. >> i'm trusting you guys with like, my life. >> his plan was to get away with this. his plan was never to be caught. >> reporter: 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 degree murder, did the jury reach a verdict? >> yes, we did. >> what is your verdict? >> guilty. >> reporter: you hear guilty. what's that moment like? >> relieved. >> it's a sense of relief. >> reporter: riley was sentenced to life in prison. he'll be in his 70s by the time he's eligible for parole. >> we were incredibly proud of all the investigators and all the work. we were almost more proud of noah and alex. i mean -- >> reporter: i mean, are they the heroes in this? >> i think they really are. i really do. i really do. >> reporter: lieutenant merritt, the walkers, they call you the heroes. what do you say to that? >> just did what i had to do. >> reporter: it took a lot of guts to do what you did. >> we appreciate that. >> reporter: as for emma, who used to joke that she was "kind of a big deal.” she's actually become one with tributes to her

all over town. there is a scholarship in her name at central high and a dog park dedicated to the young animal lover. >> it's just a good, fun, happy place to come and remember her and for other people to remember her. >> reporter: and here at the east tennessee childrens 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. merrit 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. >> and that's what we hope -- someone gets out of this story is awareness. >> and know what's healthy for you. >> reporter: emma may be gone but for those who loved her, the young girl still sparkles. >> she'd wanna be out there.

you know? and she'd want us to be laughin' and havin' fun. and not sit, you know, you can't cry all day. that you have to -- you still have to live life. >> that's all for this edition of "dateline." i'm natalie morales. thank you for watching. i'm craig melvin. >> and i'm natalie morales. >> and this is "dateline." >> i called my mom immediately. i just cried. i cried. i couldn't feel. my body went numb. i told her karlyn's gone. she's gone. >> she was a beautiful young mom doing important work. >> she was an intelligence specialist. >> some of her work was very sensitive. top secret. >> i believe she had top secret clearance. >> wn