campus full of students. >> we were really scared. a mysterious tweet. >> what do you think it meant? >> i don't exactly know. >> reporter: a terrifying phone call: >> my son just called me and told me he killed somebody. >> reporter: and a terrible truth. >> i didn't know how. i didn't know who. i didn't know anything. i just know she was gone. >> reporter: i'm lester holt and this is dateline. here's andrea canning with "after midnight." 3 f2 medianoche. days at the beach come to an end, students flood back to college. it's the same scene year after year, at campus after campus. and every year, there's that new bunch, the freshmen. >> i was nervous for classes the first day because, you know, i'm that scared little freshman. >> reporter: all those worries, all those questions. >> do i really have to go to these classes? and what's this teacher like? and all that kind of stuff. >> reporter: they're not quite adults, they're not quite teens. but now, suddenly, they're on their own. >> i mean, leaving home for the first time can be scary. scary for the kids. for their parents too. >> every mom has that, my baby's -- >> it's hard. >> going to college, yes. >> reporter: most of the time, kids sail through the experience. they make new friends, date new people. and move on. but there are others who are not so lucky. they are the victims of a troubling trend that's caught the nation's attention. dating violence. >> it could happen to anyone's daughter? >> anyone. this could happen to anyone. >> reporter: it was late september, 2012. the college at brockport, a state school in western new york, was well into the new school year. 18-year-old alexandra kogut was having the time of her life. >> as soon as i met her, i knew we were the perfect match for each other. >> reporter: alex kogut and samantha turner met within days of arriving on campus, besties from the beginning. >> you really clicked with alex. >> i do. >> right away. >> i did right away. >> why did you like her so much right away? >> i liked her because i could act so funny in front of her and i could act myself. if i had a problem, she was always there for me. >> reporter: by late september, alex and samantha were inseparable, swapping clothes and confidences. >> sounds almost like you were sisters. >> pretty much. every second i saw her, we would have fun and laugh together. every possible thing just made our relationship grow stronger. >> reporter: but on friday, septey were going off in different directions. samantha was heading home to see her family. alex was staying on campus, counting the hours until her long-time boyfriend arrived for a weekend visit. that afternoon, alex went down the hall to samantha's dorm room to say good-bye. >> it was around 3:00 maybe. and i was about to go home. and she's, like, "can i pick out some clothes in your closet?" and i was, like, "sure." so, she took three of my shirts and a pair of my shoes. and she was all excited. she's, like, "clayton'll be here in a half an hour." >> reporter: twenty-one year old clayton whittemore was alex's boyfriend. and he was coming to spend the weekend. but first, alex had a swim team meeting. >> reporter: she'd been swimming since high school, where paige whitney was the captain. >> you were the captain of the swim team. but you call alex more the heart of the swim team? >> yeah, definitely. in high school, she definitely wasn't the fastest on our team. but she was one of the most important people on our team because she had the most heart. she would be behind you at every single one of your races cheering you on, wishing you luck. >> reporter: now paige and alex were teammates again. >> she must've loved knowing that she had you to lean on? >> i feel like there was definitely that sense of security. >> reporter: that friday, the team meeting ran late. alex's boyfriend got to town before it ended. alex texted to apologize that she wasn't there to greet him. "please don't kill me" she wrote. "no worries" he answered. soon the two got together, with a busy night ahead of them. midway through the evening, samantha texted alex. >> and i told her, i was, like, "can't wait to see you tomorrow. love you, good night." you know, and then she said the same. >> reporter: but later, in the early hours of saturday morning, samantha was awakened by a call. alex's mother was on the line. what in the world was up? >> she was scared. she didn't know where alex was, what she was doing. she had a sign, i don't know how. something was wrong. and -- >> her mother-- >> her mother contacted -- >> just thought something was wrong? >> yes. >> and called you? >> yes. freaking out. and i was, like, "i'm home. i don't know." >> reporter: a fearful mother on the phone in the middle of the night, searching for her daughter. what had happened to set her off? why was she so distraught? sandra whitney is a good friend of alex's parents, becky and mark kogut. she's paige's mom. >> the koguts, they had gone off for a weekend vacation. and they had been texting that evening, and becky was sending her pictures of their hotel room. you know, you get to a hotel, hey look!e tried over and over again. and she didn't respond. and that's not how their relationship worked. you text, you call, you always responded. >> is that unusual, though, that she wouldn't respond in -- in college? it's a weekend, her boyfriend's coming for the weekend. >> i imagine the first couple times, maybe she wasn't concerned. but when it was several, that's what raised flags, with becky. >> was it a little bit of mother's intuition, do you think? >> i imagine it was. >> reporter: alex's mom worked the phone frantically, trying anyone who might know where her daughter was. finally, at 2:42 a.m., she called the campus police to ask them to go to her daughter's dorm room to check on her. officer michael johnson. >> you took that call. >> i did. >> and you headed over to the dorm. >> yes. >> and then what happened? >>well, when we went there, i knocked on the door, i knocked twice. and since it was a welfare check, i say, "well let me, let me see if this door's unlocked." >> reporter: it was. and officer michael johnson will never forget what was inside that room. >> it just seemed that something really bad happened there that night. >> reporter: what had happened in room 108? police were about to confront a frightening and confusing scene. >> you never come to work thinking you're going to see something like that. >> a young victim. but who is it? >> they were just telling everybody. you know, 'keep your door shut. don't come in the hall.' and we didn't really know what was going on. usaa. we know what it means to serve. get an auto insurance quote and see why 92% of our members plan to stay for life. hurry into lowe's and find big summer savings for this 4th of july like 5 retaining wall blocks for only $10. plus get three 2.5 quart lantanas for only $10 don't miss out on summers best savings at lowe's. everoves how they feel in dark clothes. and to keep those darks from fading there's woolite darks. it's free of harsh ingredients to help keep dark clothes vibrant for over 30 washes. for the love of darks. woolite darks. 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[man grunts] one wishful thinking, right? but there is one step you can take to help prevent another serious disease- pneumococcal pneumonia. one dose of the prevnar 13® vaccine can help protect you ... from pneumococcal pneumonia, an illness that can cause coughing, chest pain difficulty breathing and may even put you in the hospital. prevnar 13 ® is used in adults 50 and older to help prevent infections from 13 strains of the bacteria that cause pneumococcal pneumonia. you should not receive prevnar 13 ® if you've had a severe allergic reaction to the vaccine or its ingredients if you have a weakened immune system, you may have a lower response to the vaccine. common side effects were pain, redness, or swelling at the injection site. limited arm movement, fatigue, head ache muscle or joint pain less appetite, chills, or rash. even if you've already been vaccinated with another pneumonia vaccine, prevnar 13® may help provide additional protection. get this one done. ask your healthcare professional about prevnar 13® today. officer michael johnson, a cop at the college at brockport, was on a routine welfare check at a dorm room early one saturday in september, 2012, when he got the shock of his life. >> we don't see that level of violence that often. >> reporter: room 108 was wrecked. there was blood everywhere. on the bed, on the door, on a pillow on the ground. and in the center of the room, was a young woman, lying on the floor, face-down, her bloody hair falling over her face. >> it seemed very unnatural the way she fell, the blood splatter that was in the room, even the bloody footprints that were around her, all indicated that something violent had happened in that room. >> what feeling do you have when you when you see something like that? >> well, the adrenaline kicks in and luckily, you know, you need that adrenaline at that moment. and it was just time to go to work. and if she was alive, i had to do all i could for her. >> reporter: officer johnson knew he needed help fast. >> i heard this guy yelling. and i thought it was a drunk college kid. >> reporter: hailey plymale lived across the hall from alex's room. the commotion woke her up. >> and i noticed the man, was like yelling for help and stuff. so i woke up and i started looking my peephole. and it was a police officer yelling. >> reporter: lieutenant daniel vasile works with officer johnson on the campus force. >> he radioed me for the a.e.d., so -- >> what's a a.e.d.? that's the defibrillator. >> okay. >> so, i arrived. i grabbed it. i went running to his location. >> what did you think when you saw what you saw? >> i couldn't believe it. i guess, you know, you never come to work thinking you're going to see something like that. >> reporter: hailey plymale was now glued to her peephole. she saw residence officials everywhere. >> they were just telling everybody, you know, "keep your door shut. don't come in the hall." and we didn't really know what was going on. >> reporter: the news was spreading. hailey was fielding a storm of texts from worried students. >> everyone was just so confused. and it was all just like, "i don't know, you know. i think somebody's hurt. but i don't know what's happened." >> reporter: by now, the cops realized the young woman on the floor was dead. hailey soon learned that too. >> what happened was the ambulance showed up. and the police officer said to the paramedic, "we only need one of you to go in and to pronounce her." and the paramedic went in and came out, pronounced her jane doe. and it was just, like, "oh, wow." i knew that that meant that they couldn't identify who it was and they left. and i woke my roommate up. and i said, you know, "somebody's died." and she didn't believe me at first. and i told her, you know, "like, they left. the stretcher-- had nobody on it." >> reporter: the students, on their phones, tried to stay calm, but it wasn't easy. after all, a college residence is supposed to be safe. but now there might be a killer on the loose. >> we were really afraid. and, i mean, the police officers were like, "you're okay. like, we're here. you're safe." but we were really scared. >> reporter: hailey went over and over the events of that night in her mind. and she remembered something. about 1:15 am, as she was trying to go to sleep, an unusual sound. but was it related? >> it was, like, like, little, like, thud, thud. and then, it was, like, maybe, like, a pause. and then, it was, like, thuds more. and then, like, kind of another break. and some of them were louder than others. >> reporter: now, as the activity in the hallway intensified, hailey heard a line straight out of a cop show. >> the police officer said, "this is now a crime scene. nobody touch anything." >> so at that time, i knew that we had to just do our jobs and we had to preserve everything, you know, for the safety of the rest of the campus. >> reporter: the officers had a million questions. number one, who was the girl lying with her face to the floor? alex kogut, the girl they'd been asked to check on, had blonde hair. there were pictures of her in the room. the girl on the floor was a brunette. was she alex's room-mate? it was hard to know, her face was bloody, unrecognizable. >> so, then you must be wondering, well, where's alex? >> right. >> yes. >> reporter: the cops learned that alex had entered the dorm with her boyfriend after midnight. and then they made a startling discovery: when they looked closer at the photos in the room, they saw a young man they recognized. in fact they'd issued him a ticket that very night. >> so we knew who we wanted to look for at that time. >> reporter: it was clayton whittemore, alex's boyfriend. they needed to find him, and fast. he might lead them to alex. >> if we have someone that did this violent act here in this specific room, you know, what is he capable of doing when he leaves here? coming up, a missing boyfriend. an anxious best friend. >> i left here. >> 4:00 in the morning? >> 4:00 in the morning. >> and a mystifying murder. >> there were so many things that didn't make sense in the room, it was very hard to say, okay, this is what happened. case closed. >> when ""dateline" continues. when you got married? when you had kids? family isn't defined by who you love, but how. tylenol®. let's worry proof our walls. with paint made to stand up to this... and look beautiful for years. let's do this. right now get $10 bucks of one gallon cans of behr paints and stains. the home depot. more saving. more doing. you wish your dog could fight off fleas and ticks. but since he can't you rely on frontline plus. its deadly killing force kills fleas and ticks, plus flea eggs and larvae, preventing a new infestation. frontline plus. the vet's #1 choice. developing some of the highest quality nutrition isn't easy so at gnc, why do we do it? why do we work to deliver clinically studied products to fill the world's nutrition gaps? why do we insist on the most stringent quality checks period? well, here's why... ♪ ♪ celebrating 80 years of quality life and quality products. and we're just getting started. gnc. >> reporter: the campus cops investigating the murder in mclean hall weren't sure who the victim was, but they'd recognized a young man in photos in the dorm room. they'd seen that same young man when they were patrolling the campus earlier that night. >> i observed a couple coming down the street here on utica street. we could see that he had an open container in his hand. as he kept coming, we intercepted him right here on the sidewalk. i requested his i.d. i could see that it was an open beer can. and i explained to him that we have a local ordinance here that says that you cannot have an open container. >> did he seem angry, was he agitated? >> no, he was actually-- >> did he -- >> very cooperative. so i gave him the ticket and they started to walk away right down the sidewalk right here. >> reporter: the young man who got the ticket was clayton whittemore, returning home from a party with his girlfriend, alex kogut. >> and when they left, did they seem fine? >> they seemed normal to me. >> in fact, i was even doing small-talk with the female that he was with, and was able to make her laugh a little bit, so if anything was bothering her, she didn't let us know. >> so, just a normal couple out on a friday night. and wasn't quite the last of him? >> no, as he, as they both started walking away i observe him drop the beer can. and he just dropped it right onto the ground. and i made a comment that that could be another $100 fine. and he did comply and he went back and he picked it up and after doing that, that's when i saw him cross the street here. and the same time, the female stayed on this side of the street. and then they both continued to walk on separate sides of the street. >> reporter: alex and clayton had been dating for a year and a half by then. they were both from the town of new hartford, in central new york. they got together when alex was in high school. he'd already graduated. now, they were trying to make a go of a long-distance relationship. >> they really wanted to make it work and stuff. and i think it was working. i think she really did love him. >> what kinda things did she say to you about clay, describing him or the time they spent together? >> it was kind of just little things here and there. like, "oh, i can't wait to see him." like, "i miss him." you could just see it in her eyes, that she really did want to be with him. >> reporter: clayton, number 21, had been a stand-out hockey player in high-school. after he graduated in the spring of 2010, he spent a season playing for a college prep team in florida, living with a host family there. >> he was like the star player. he was the guy that scored the goals. >> reporter: hunter fernandez, one of clayton's teammates, lived with the same host family. >> paint a picture of clayton for us. >> he was hard working. he was a really nice guy. he was funny. we always had a good time. >> did you guys ever get into a little bit of trouble? >> no we never really got into trouble. we were, we were always busy. >> what about girls? did you hang out with girls? or was there time? >> nope. >> partying? >> never. >> drinking? >> he drank once. >> this sounds like the tamest bunch of hockey players i think i've ever heard of. >> yep. >> reporter: it was hardly surprising that alex was drawn to another athlete. and clayton was a catch. paige whitney, alex's swim team pal knew that. she'd gone through high school with clayton, sat beside him in senior year math class. >> she felt like he deserved a lot more and that she was very, very lucky. >> really? >> yeah. >> so she considered herself lucky that he had chosen her? >> absolutely. >> watching them together, did it seem that he really cared about her, that he really liked her? he was -- >> absolutely. >> happy to be in that relationship? >> yeah, you know, you see them laughing together. you see them, you know, getting along so well. >> reporter: their twitter messages were light-hearted. they called each other "dork" and "freak" and lived out their lives in the twittersphere. before clayton arrived that friday, alex had tweeted "ahhh see you soon." her family liked him, too. they'd given him a care package for her; and her mom had contributed $20 towards gas for the trip. >> reporter: once alex's swim team meeting ended that day, the couple met up, had some alone time in her dorm room, then went to dinner. alex and samantha were texting of course. >> i asked, you know, like, how she was doing, what she was doing. and she's, like, "oh, well, we're out to dinner right now." and then they went out to a friend's house. and then they came back to the dorm. >> reporter: on the way back, clayton got that ticket, and the cops saw the two walk away separately. then at 12:13 a.m., alex posted a cryptic tweet. "should've known" it read. "should've known." >> what do you think it meant? >> it probably does have something to do with clayton, but i don't exactly know. >> reporter: minutes later, alex swiped her card to enter her dorm with clayton. it was 12:17 on saturday morning. so now investigators were desperate to find out where clayton whittemore was. and whether alex was with him. >> luckily, we had all his information from the ticket that lieutenant vasile issued him. >> reporter: but clayton had been a model of co-operation then. what could he tell them, if anything, about what had happened in the dorm room that night? >> what's your gut telling you happened? >> i couldn't put together what happened because it was so violent. there were so many things that didn't make sense in the room that it was very hard to just say, "okay this is what happened, you know, you know, case closed." >> what were the scenarios that you were thinking of? >> maybe there was an altercation between the roommates. maybe, possibly alex and clayton were on the run and this was the roommate that was on the ground. maybe alex was abducted by clayton. maybe clayton had hurt the roommate. >> a lot of things are running through your mind. >> yes. >> reporter: lots of things on other people's minds, too. at her parents' house, samantha turner, alex kogut's best buddy, was phoning all her friends. when she got through to her roommate, a college official got on the line and told her "there was a situation." >> and then i broke down. and i grabbed my sister and i was, like, "we need to go to brockport now." and then i rushed here. >> at 4:00 in the morning? >> 4:00 in the morning. and got here, saw the police cars. >> you didn't know at this point what had happened still? >> i didn't know exactly who it was. >> reporter: hundreds of miles away, a frantic mother waited, desperate for answers. but when those answers came, they would be unbearable. and they were coming soon from the killer himself. coming up. two frantic phone calls from a mother. >> he said she was breathing and then she said. >> and her son. >> what's going on there, bud? >> i just -- i did something. and one more step towards a healthy tomorrow. invest in your heart health, with kellogg's raisin bran no crying today... and try new kellogg's® raisin bran with cranberries. the tart and sweet way to up your breakfast game. >> reporter: early that saturday morning, steven peglow, a veteran homicide investigator with the monroe county sheriff's office, was called to the brockport campus. the cops there had a murder on their hands, a body they couldn't identify and a killer on the loose. >> everyone thought they knew what was going on, but nobody really did. and until you got there and started to put the pieces together, you didn't know. >> reporter: as he drove to the campus, investigator peglow reviewed the facts as he knew them, one young woman was dead, another was missing. >> what had been reported was that there was a young lady still alive and that needed help, right then that was, that was my priority in my mind on the way out there. >> were you thinking that clayton had taken alex and had hurt her but she was still alive? or that -- >> yeah. >> someone else may be involved in the whole thing? >> at that point, i was thinking that she was just with clayton and he had hurt her. >> so you're thinking we have to find her immediately. >> yes. >> reporter: but five counties away, a drama was unfolding that would break open this case. about 3 a.m. an operator at the oneida county emergency center got a call from a profoundly troubled dad. >> yes, uh, my name is scott whittemore and my son, clayton, just called me and told me he killed somebody. >> reporter: it was a stunning statement even for a 911 dispatcher in the early hours of a saturday morning. but the dad didn't know much. >> ok, where did this happen? >> i don't know. >> where is he right now? >> i don't know. >> reporter: the father reported that his son was in a bad way. >> he's talking about killing himself too. i don't know what's going on for them to not, except that he got in trouble. >> reporter: the divorced dad admitted that he was out of the loop about family matters. now he was doing his best to stave off a tragedy. >> do you know if he has any weapons? >> i don't know. he did ask me for one i have. i have a permit for a pistol he asked me for one. >> and he asked you for your pistol? >> yes. he doesn't have it. >> and did he say what he wanted to do with it? >> kill himself. >> reporter: the dispatcher asked scott to call his son back to find out more. minutes later the father was back on the line. >> hey scott. what's up? >> he has a girlfriend out in brockport. his mom thinks he's probably on his way home from brockport. >> reporter: the 911 dispatcher got clayton whittemore's mother on the line. >> hi sandi? >> yes? >> we're trying to find your son. you think he was out visiting his girlfriend at suny brockport? >> what, well he -- he's in canada right now. >> well he's not in canada. >> he's not? >> no. at least his cell phone isn't in canada. if you were just talking to him on his cell phone he's not in canada. >> yeah, okay. >> okay just take a couple deep breaths and, and try to, we're going to try to find him so we can get him some help. >> reporter: the dispatcher got the name alex "kogurt" from the stressed out mom. slightly wrong but it was enough. seconds later, he was on the phone to the campus cops in brockport, and now, finally, the pieces of the story began fitting together. >> we got a call from a father about an hour ago that said his son called him he and stated that he killed somebody. >> okay, okay. >> we pinged his phone and the son's name is clayton whittemore. >> okay. >> and apparently he's out there with his girlfriend, an alex kogurt at your college. >> yeah, that's who we're looking for. >>: oh you're looking for him? as well, huh? >> yeah we actually had him earlier on an open container at midnight. >> yeah, how's the, is the girl okay? i mean we're just, we're kind of concerned on what's going on. >> no, well the, the uh, we don't know where this alex kogut is. >> okay. >> we can't locate her, but her roommate is a doa. >> reporter: that's the theory the campus cops were acting on: that the roommate was dead and alex was with clayton somewhere. but then, new information from clayton's mom. clayton had just called his sister and told her a frightening story about alex. >> and she said something like he said she was breathing and then she stopped. >> and he said the girlfriend stopped breathing? >> yeah. >> reporter: clayton's mother was beside herself. >> did you get a hold of the college out there? >> yeah they're looking for him. we don't know what the heck's going on, so everybody's out looking to see if they can find them and make sure they're okay. >> reporter: and then once more that morning the call-line lit up at the 911 center in oneida county. this time it was the call everyone was waiting for, clayton whittemore was on the line. >> what's going on there, bud? >> um, i just, i did something. >> reporter: it was 3:44 am. the horror of what had happened in room 108 would soon be revealed. coming up: who had clayton whittemore killed? >> i didn't know how. i didn't know who. i didn't know anything. i just know she was gone. >> when "dateline" continues. help relieve pain stop further joint damage and clear skin in many adults. doctors have been prescribing humira for nearly 10 years. humira can lower your ability to fight infections, including tuberculosis serious,sometimes fatal infections and cancers, including lymphoma, have happened, as have blood, liver and nervous system problems, serious allergic reactions and new or worsening heart failure. before treatment get tested for tb. tell your doctor if you've been to areas where certain fungal infections are common and if you've had tb hepatitis b, are prone to infections, or have flu-like symptoms or sores. don't start humira if you have an infection. visit humira.com and talk to your rheumatologist. humira. this is a body of proof! seriously? 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[ chuckles ] worst apocalypse ever. protecting you till the end. now, that's progressive. ♪ hi! what happened to your hair? i got it. walgreens has all you need to keep it all under control. from a little touch-up... come on, guys! to finding that perfect finishing touch... to making memories at the touch of a button. all without missing a beat. walgreens. at the corner of happy and healthy. >> reporter: clayton whittemore was at a rest stop on the new york state thruway when he called 911 with a stunning admission. >> i'm turning myself in. um, i just, i did something that i can't take back and just got to turn myself in. >> reporter: it was almost 4:00 a.m. a frantic hunt that had pulled in multiple police agencies, emergency dispatchers, college officials, and two sets of anguished parents was almost over. >> there were two officers, two new york state troopers who,you know, were patrolling the thruway that night. >> reporter: sandra doorley is the district attorney of monroe county in western new york. >> they were called to respond right to that dewitt road service area, not knowing what to expect. at that point, it was one dead on the brockport college campus. and perhaps another missing. >> and clayton was there waiting? >> he was. walked over and said "i'm turning myself in." they notice, you know, bloody sneakers and they notice blood on his hands. >> reporter: within seconds, 21-year-old clayton whittemore was cuffed and in custody. now for his car. what could it tell them? >> they wanted to check the trunk. they didn't know if there was a body in the trunk. because at that point, they still hadn't determined, you know, who it was actually on the dorm room floor of room 108. >> reporter: that was about to change. the cops back in brockport, who initially thought the victim might be alex kogut's room-mate, had learned the room-mate was staying elsewhere that night. but where? they started an urgent search. until they spoke to her, they couldn't be certain of the victim's identity because of the hair color. investigator steven peglow. >> the girl lying on the floor had very dark, almost black colored hair. and when you saw the photos that alex had put up in her dorm room of her and clayton, she had much lighter hair. the roommate had darker hair. >> reporter: investigators knocked on students' doors, questioning them. then a nugget buried in a conversation. they learned that alex had recently dyed her hair brown. they had what they needed to i.d. their victim. now they wanted to hear from just one more person, alex's room-mate. when she did call in, finally, they learned she'd been staying in another dorm room. >> we had her come to us, so that we could speak with her, then we were positive. >> reporter: positive that the girl on the dorm room floor was alex kogut. bubbly, happy, lovely alex. only 18 years old. best buddy samantha turner, who had rushed back to college early that morning, was devastated. >> i just, i broke down. and i knew at that point my life was changed. >> and you, you just knew what had happened. >> i just -- >> without anyone even -- >>i just knew. >> telling you? >> uh-huh. i didn't know how. i didn't know who. i didn't know anything. i just know she was gone. and i could never see her again. >> reporter: sandra whitney and her daughter paige are family friends of the koguts. paige, remember, was a student at brockport too. her roommate woke her up around 7 that morning. >> and she said, "we have to go. we're all meeting together. something happened." >> paige called me. and she said, "something happened to alex." i said, "alex -- what?" she said, "oh, it was a terrible accident." and i said, "well, is she okay?" and she said, "no." i said, "is she in the hospital?" and she said, "no, mom -- she's not." and i said, "has she died?" and she said, "yes." so, i was shocked, and all i could think was, what could've happened to alex in her dorm room? >> reporter: the new york state police were asking clayton whittemore that very same question, that very morning. >> were there problems with your relation, you guys, i mean, your relationship or -- >> no. we were good. >> reporter: clayton put the pieces together for the police about what happened that night and it began with the fact that his relationship with alex wasn't so good after all. the couple had dinner. then the party. clayton said he and alex drank moderately. but at the party he got annoyed with her, said he felt disrespected. >> when i'd say anything to her, you know, she'd, like, raise her voice or something. but if anybody else said anything to her, she'd be all smiley and giggly. >> reporter: as they walked back from the party, clayton got that open container ticket. >>: so, i was already aggravated and it aggravated me more. >> reporter: clayton, remember, walked to the other side of the street to cool off. and then alex posted that final cryptic tweet, should've known. >> we'll never really know what that meant. but -- >> what do you think it meant? >> should have known that, you know what, "maybe we weren't meant to be together. maybe we should break up." >> reporter: at 12:17 am, alex swiped into her dorm. she and clayton entered her room. clayton said they were fighting about cheating. "old stuff" he called it. >> what was she saying? >> she's like, she's like, "i saw a picture on your phone," way back, you know, november of last year or something. >> yeah. >> and, you know, it'll be a picture of my, my sister, for god's sake. >> reporter: then, he told the cops, she got physical. >> she started pushing me and pushing me and pushing me. she kept doing it. and, uh -- >> was she saying anything when she was pushing you? >> uh, the same stuff, you know. >> reporter: but, the investigator pointed out, clayton was a strong guy. alex was tiny. >> you didn't feel threatened by alex tonight, it was more than that right? >> i don't even know what it was. >> don't know how to explain it? >> i don't know if it was my temper, or just her hitting me in general, or pushing me and stuff. >> but you're not hurt, right? >> no. >> she didn't hurt you at all, right? >> no. >> reporter: he told the cops he asked her to stop. but, he said, she wouldn't. and when he offered to leave, he said, she told him to stay. and then this. >> all of a sudden, i just snapped. >> mm-hmm. >> i hit her back. >> where'd you hit her back? >> threw her up against the wall. >> reporter: the attack that followed was savage. unthinkable. in a tiny dorm room, surrounded by sleeping students, clayton whittemore beat his girlfriend to death. >> reporter: investigator peglow has seen plenty of homicide scenes. but never one like this. >> there was a few of us in the room. and people were like, "okay, well i have blood on this. okay, i have blood on this." and gave you an idea of the rage that had gone on in that room. >> reporter: peglow, who has studied the interview video, says there's one thing he can't forget. clayton told police that near the end, he realized alex's breathing had become labored, that the girl he said he loved, was dying. >> you know it was like watching an animal suffering. >> ok. >> and die. >> yup. >> you know? that's why i did the other stuff that i did. because, you know, someone you love, i'm not going to watch them sit there and suffer. >> yup. ok. >> that's why i did it. >> so, you see her suffering, and you think she's going to die? is that right? >> yeah. i didn't even think, getting help. >> reporter: didn't get help. didn't call an ambulance. didn't occur to him. instead he hit her until she died. to put her out of her misery he said. >> must've seemed almost impossible, how could she be murdered? >> exactly. disbelief, shock. it's not real, it's not real. that doesn't happen. you don't go away to college and suffer that. you just don't. >> reporter: clayton whittemore was charged with second-degree murder. he pleaded not guilty because clayton whittemore had an explanation, and his attorneys would reveal it at trial. >> reporter: coming up:could anything explain such violence? >> it happened my entire life. >> yeaa lot of it, huh? >> i saw it all. >> reporter: the verdict... when before fibromyalgia, i was the go-to person. i was energetic. then the chronic, widespread pain drained my energy. my doctor and i agreed moving more helps ease fibromyalgia pain. she also prescribed lyrica. for some patients, lyrica significantly relieves fibromyalgia pain and improves physical function. with less pain, i feel better. lyrica may cause serious allergic reactions or suicidal thoughts or actions. tell your doctor right away if you have these, new or worsening depression or unusual changes in mood or behavior. or swelling, trouble breathing rash, hives, blisters, muscle pain with fever tired feeling or blurry vision. common side effects are dizziness, sleepiness, weight gain and swelling of hands, legs and feet. don't drink alcohol while taking lyrica. don't drive or use machinery until you know how lyrica affects you. those who have had a drug or alcohol problem may be more likely to misuse lyrica. with lyrica i have less fibromyalgia pain and can keep moving forward. ask your doctor about lyrica. let's worry proof our walls. with paint made to stand up to this... and look beautiful for years. let's do this. right now get $10 bucks of one gallon cans of behr paints and stains. the home depot. more saving. more doing. does your makeup remover take it all off? 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>> you know, our theory that night was that his anger was just building, building and perhaps fueled by alcohol. >> reporter: prosecutors tried to show that clayton whittemore had already established a pattern of violence. they called ex-girlfriend melinda graniela to testify about one scary episode. >> we were fighting in a parking lot and he had choked me. and he kind of held on for a few seconds. i thought that he might not stop. but eventually, he did. and i locked him out of his car to cool down, and he did. and it kind of blew over. >> but that one was serious. >> yeah, it was scary. >> reporter: hunter fernandez was also called to the stand. hunter had played hockey on that college prep team in florida with clayton. hunter, too, had a scary experience. it happened after clayton drank a half dozen beers. the one time hunter says, that he saw his teammate drink. >> he walks in the kitchen. then he grabs a knife and he raises it above his head, he looks like he was possessed. he just took a step towards us. and our host mom sees what's happening and she's like, "clayton, put the knife down." >> reporter: defense attorneys didn't dispute that clayton whittemore killed alex kogut. didn't even try. and they didn't dispute that his anger was years in the making. but, they argued, this wasn't a case of murder. their client was guilty of the lesser charge of manslaughter. why? they said he was under the influence of extreme emotional disturbance when he killed alex kogut: because clayton whittemore was a victim himself. >> you know i'm turning myself in for what i did. >> okay. >> the man who called you is the man who should turn himself in. >> reporter: that's clayton talking to the 911 dispatcher, hours after the murder. he's talking about his dad. telling the dispatcher his father had abused him and his family for years. >> it happened my entire life. >> yeah. so you said you saw a lot of it, huh? >> i saw it all. i watched my brother get beat with a baseball bat by my own father. i watched my own father break my sister's nose, throw my own mother down to the ground. and beat her. i watched him try to shove a remote controller down the throats of all his children, for fingerprints on his car. >> reporter: the cops in the interview room asked him how he felt about his dad now. >> do you and your dad have a relationship now? >> not really. my family, not like people i'm really close to. growing up with my dad, one man i despised. >> your dad? >> reporter: in the minutes before he was arrested, clayton wrote a bizarre apology to alex and the koguts. "sorry to the family and you" he texted. "nothing will ever fix or undo what i did. i became my father. in court, clayton's sister took the stand and supported her brother's story. their father, scott whittemore, did not respond to dateline's calls. there's no record of complaints against him. but a defense expert, a psychiatrist, testified scott admitted that as a former marine he may have been rough. because of that abuse, the expert concluded that clayton was suffering that extreme emotional disturbance and snapped in the dorm room. the prosecution begged to differ. >> it's just sad and tragic. and you know what, we never discounted or denied his past. but that doesn't excuse what he did. >> reporter: three weeks after the trial began, the case went to the jury. the verdict was swift. guilty of second-degree murder. >> i just felt this overwhelming sense of relief, that the truth came out, and that there was, there was finally a verdict. it was the right verdict. >> reporter: alex's mom did not attend the trial but followed it closely and tweeted. >> becky kogut, after the verdict, tweeted, "justice for my beautiful baby." did you talk to her? >> oh yeah. >> about the verdict? >> uh-huh. >> and what did she say? sandra whitney: >> it was, it was a private conversation between two moms. there were tears, of course. doesn't bring back alex. it doesn't. >> reporter: clayton whittemore was sentenced to 25 years to life. now, among those who know the story of alex kogut's life and death, there is a new awareness about the vulnerability and challenges of young love. especially because, prosecutors say, there was evidence to show clayton had a history of threatening alex. he left angry voicemails on her phone. assistant district attorney meredith vacca. >> there were almost 30 voicemails that she saved from him. they were all of that aggressive, controlling nature, is what we argued to the court to seek admissibility of them at trial. >> reporter: the voicemails were not admitted in court. but prosecutors read an excerpt for "dateline," editing out the expletives. >> i'll kill you next time i see you. you're a slut and a skank. so don't call me. i'm sick, i'm sick of you." and i left a lot of words out. >> when you add in those expletives it is really hard to hear? >> it was. these were voicemails that really were scary. >> reporter: those close to alex and her family say they never knew about the voicemails. never knew there was a problem. they say there were no red flags about clayton whittemore. >> that's why it's out of the blue. never saw that coming. >> nothing. totally, totally, caught me off guard. >> reporter: perhaps, for parents, there is a lesson to be learned: ask questions, know what's happening, even if there are no warning signs. >> even if they might be not wanting to talk about it, you know, ask those questions. >> reporter: after alex died, sandra whitney and her family started the purple pinkie charitable foundation to campaign against dating violence. purple symbolizes the fight against domestic violence, it was also alex kogut's favorite color. sandra came up with the idea as she comforted alex's former teammates. >> and i said, "so paint your pinkies purple, and this is for alex." you have more strength in your little finger than the worst thing that can come at you. >> reporter: two years later, there were still purple ribbons in alex kogut's hometown. still friends tending a college memorial to honor students who have died, at a college that has itself had to heal. a college that has since opened a center to raise awareness about dating violence. and there are still those, like paige whitney, who will never let the memory of a graceful, joyous, young spirit fade away. >> for the rest of my life, whenever i see purple i will think of her. whenever i hear a story of any type of domestic violence i will think of her. and i will not stop telling her story. 3 f2 y no voy a detenerme. blank wlank right now at 11: cracking down on illegal fireworks. the serious danger during the drought. . right now at 11:00, cracking down on illegal fireworks. the serious danger during this drought. good friday evening. >> i'm jessica agurre. illegal fireworks combined with dry conditions could trigger a dangerous blaze.