in the pit of my stomach i just knew, something's not right here. i just felt something bad had happened. he must have been so, so scared. >> they were so happy at first. >> kevin just fell in love with her. morgan was very, very charming. >> but when the marriage went bad, he went missing. >> he just disappeared. >> was this a husband who didn't want to be found? was this a wife who had something to hide? >> they are getting in the truck. they are leaving. >> what had happened behind closed doors? >> she laughed and said, no, there's no affair. >> someone was keeping secrets and even police couldn't wrap their heads around this one, until they found it, a trail of texts.

>> we were like, holy smokes, it's right there. >> it sure was. every stunning detail. >> snapple iced tea seemed like the perfect tool to put the poison inside. >> was this a loving spouse or a lethal one? police were in for a killer surprise. >> i felt like the gates of hell were opening. >> i'm lester holt and this is "dateline." tonight, hoda kotb. >> how much do we reveal to the ones we love? do we keep our betrayals hidden behind closed doors? or do we hide in plain sight, masking our deeds with words? >> a text message that says, i'm fine, just clearing my head. >> that was kevin mengel for a time, clearing his head, he told his family and friends. facebook status, wants to be left alone.

>> maybe he just had enough and took a vacation for himself. >> but there was a trail of electronic messages that seemed to tell another story. a far more sinister one. >> we were floored when it was all there for us to read. you can't make this stuff up. >> which was fact and which was fiction? >> these text messages don't even seem real. like they just don't seem real. >> long before kevin mengel had a cell phone or a facebook page, he was a suburban high school guy with a sister to worry about. >> he was the typical brother. he would follow me around and tell guys not to talk to me and things like that. >> was he being protective? >> very protective. >> for as long as michelle can remember, kevin mengel was a family man. a big brother who felt he needed

to look after his younger siblings after their parents divorced. >> kevin had a terrible time with it. always told us he would never get a divorce. he would never get a divorce. >> instead, kevin looked for the perfect romance. >> he was managomous? >> yes. kevin was very committed and gave it his all. >> kevin was 20 when he met the one, his forever girl, morgan from a few towns away where she graduated from an exclusive girl's school. >> morgan was very charming, very sweet, very attentive to him. came over to the house to hang out with me. >> outgoing and charismatic, morgan made an effort to win over kevin's friends, too. >> very nice, very upbeat, very friendly, always smiling. >> and kevin, well, he fell hard for morgan's charm.

>> he just -- he loved her. >> he was head over heels for her. >> so kevin was about to get what he had always wanted. a wife and kids. but just not in that order. morgan gave birth to their first child a few months before they got married. still, theirs was no shotgun wedding. the young celebrated in traditional style. >> kevin was on top of the world. >> the perfect picture, wasn't it? >> it was the perfect picture. >> kevin loved being a dad and he and morgan had two more children but his relationship with his own father was rocky, had been since his parents' divorce. >> we were boast stubborn and pig head. he didn't call me, i didn't call him and we got into a little battle. >> years went by? >> and years went by. >> but by june 2010, kevin and his dad had patched things up, grown closer than ever. they made plans for the whole family to celebrate father's day together. >> he was so excited, he said to

me, dad, i can't wait to come out for father's day and i said, i can't wait to have you. i said, i love you and this is so wonderful. >> he just seemed to be at peace that i had not ever seen him at. >> then, it was the morning of the father's day party when it happened. sister michelle called their mom to check in. >> she didn't sound right. and i said, are you okay? and she said, kevin left. and she just started crying hysterically and she said, kevin left, kevin left. and i said, mom, something's not right here. >> uh-huh. >> he left the three kids, he left morgan, i don't know where he went. he just sent me a text message. >> kevin, the till death do us part romantic leave his wife and kids? perhaps morgan put it best when she typed out their father's day regrets to kevin sr. >> we received a text message from morgan, due to unforeseen circumstances, we will not be able to be there today. happy father's day. >> unforeseen circumstances?

what exactly did that mean? >> we all knew how excited he was before father's day. it would be the one that he would not miss, no matter what happened. >> no matter what happened. where had kevin mengel gone? >> so, we know that kevin's family was concerned. but the police, not so much. when we come back, we'll hear from investigators. >> there was no reason to believe that anything had happened to kevin. >> and we'll learn that maybe there was a reason for kevin to hit the road. >> i thought morgan was having another affair. ♪ every day, as always, there's a lot to love for a little on mcdonald's dollar menu. ♪

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when kevin mengel was a no-show for the family barbecue on father's day, his sister michelle was disappointed and more than a little confused. >> he had called my husband to say how excited he was to spend father's day that sunday with all of us. >> so it was supposed to be a big father's day celebration? >> a big father's day and he couldn't have been more excited. >> kevin's younger brother chris also knew how forward he was looking to being with his family. after all, kevin had just reconciled his father after many rocky years. >> i thought, man, this is odd. why would he do this now? it doesn't make any sense. >> the story morgan the wife told is that kevin had taken off, told her that the marriage was over.

in fact, by father's day, he had already been gone for two days. >> kevin's fine, he's clearing his head. >> what do you mean kevin's fine? >> he's fine. he just had to get away and clear his head. >> she's trying to tell you that he needed space? >> he needed space. >> i can see him blowing off and taking off and saying, i'm just going to get away. so that part of me said, okay, he just did that. he's going to come back in here today, tomorrow, whatever. >> so be patient and wait? >> just be patient. >> patient, because those close to kevin and morgan had seen the couple's ups and downs before. their breakups, in fact, were almost an annual event. >> it was like clockwork. every august around their anniversary, we would expect the phone call that morgan picked up and left and kevin would call us crying hysterically. he would be just completely distraught. >> he said, i love her. i can't help it. i love her. >> and soon morgan would return. kevin's world would right itself

and they would be as good as newlyweds for a while. >> she could act like nothing ever happened and acting all lovie-dovie sitting down on his lap. >> but what was weird about this separation was that kevin had taken off, not the other way around. >> she always took the kids and she always left. kevin never once walked out on her. >> his family worried this must have been the fight to end all fights. and it wasn't like kevin not to call his family for support. the only person he reached out to was his mom. a few days after he disappeared, he sent her a cryptic text message that seemed to alarm her more than put her at ease. and so kevin's mom did something that seemed a little drastic, she called the west goshen police to report him missing. >> we thought maybe he was overreacting to kevin leaving. >> detective david maurer. >> there was no reason to believe that anything had happened to kevin.

she was receiving text messages from kevin's phone. >> their feelings were, if somebody is communicating with him, then he's not missing. >> kevin's dad agreed. >> i was a little concerned that she may end up with a little bit of egg on her face because he was going to show and -- >> right. she had called the cops. >> yeah. >> and not long after that initial missing person's report was filed with the police department, an officer called the family back to say kevin had been spotted not far from his home. >> one of the officers stopped at a check cashing place right up the street from where morgan and kevin live and the owner of the check cashing place was very familiar with kevin and he saw him across the street. so that lent some credibility, also, that kevin was in the area. >> he was close to home, sending texts to his wife and mother, just refusing to see or speak to his family. and he did finally respond via text to his father. >> what did you get back? >> "doing okay. just need time away."

>> and kevin's sister received this message. >> "hey, sis, i'm fine. worry about morgan. she's the one you should be worried about." >> but morgan, it appeared, was doing just fine. the couple owned a landscaping business and monday morning morgan showed up to meet the crews and told them she was now in charge. an employee recalls she had the garage looking spotless. >> there's always oil traps on the ground. this day, you could have ate off this floor. >> but this was new, too, as al went about his monday landscaping jobs, he noticed morgan, the boss' wife, flirting with a 21-year-old employee named steve shappell. >> morgan looks at me and says, steve wonders what color of underwear i have on and steve says, yes, pink with black stripes. right off the bat. >> and when al had a question about an assignment -- >> i would call morgan and steve's there. steve's answering her phone. >> why was this kid who mowed

lawns and was barely old enough to buy a beer suddenly acting like the must man in charge? kevin's sister michelle remembered him as a quiet, unassuming young guy who had done some work on her yard just weeks earlier. >> this kid steve could not have been more polite to us. >> so what would kevin think now of his employee spending the workday at the pool with his wife and kids as michelle observed when she took a drive-by. >> i drove by her development and she was sitting out at the pool with steve and the kids. >> okay. you see steve sitting with her and you were thinking what? >> i thought morgan was having another affair. >> it was no secret among those who knew the couple that morgan had strayed before. could kevin had suspected that morgan was at it again and was that the final straw that drove him out? no way to know. he still was not taking calls. and then, five days after he disappeared, kevin finally had something to say to everyone who knew him in the most public way possible.

he posted an update on facebook. status, "wants to be left alone". >> he wants to be left alone. some of his friends backed off then. his friends were looking for kevin and after that facebook thing came, they thought it must be another morgan and kevin fight. >> but to kevin's immediate familyis facebook update was far from reassuring. to them, it was an ominous red flag. >> every other update that kevin had put on there had come from his cell phone because it shows the little cell phone and this one came from a computer. >> which seemed so odd. the family knew that kevin did everything on his cell. what's more, the wording in the text messages had he been spending just didn't sound like kevin. for example, michelle wondered, when did he start calling her "sis"? >> in the pit of my stomach i just felt like something bad had happened to kevin.

>> and if the cops would not investigate, the family decided it was time to do some detective work themselves. >> i'm afraid his wife and the new boyfriend are making their move to leave. they are leaving. >> coming up, a confrontation -- >> i said, i'm not okay with this. he just disappeared. i don't believe you. >> what would it take to did i lert the police? >> i said, would you mind coming down to the police station? i have a couple of questions for you. >> when "dateline" continues. you want big savings? check this out. hurry in to sears for our new years celebration. get up to 25 percent off all kenmore appliances plus, an extra 15 percent off all brands with sears card.

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y viento, ya había pasado una >> people gathered at my mom's house. everybody just sat there waiting. >> kevin's parents and siblings had not spoken to him, heard his voice, that is. the only communication he was making was on facebook and through text messages. >> i think i may have said in there, call me or one of the family members and he said, i am speaking to a family member.

i'm speaking to my wife and that should be enough for everybody. >> but it was not enough. because now a bizarre and horrifying thought had begun to take route and grow. the mengel family suspected that all those messages were not coming from kevin at all. >> i left another message for him saying, "can you just tell me the name of the street that we grew up on?" tell me that and i'll leave you alone. >> the police initially didn't even consider kevin a missing person but now the family begged them to take another look. >> we went back to the police again and pleaded. we tried to think of anything, the kids are home alone, she's not there, anything that we could get them to do to go over there. >> detective maurer agreed to stop by the apartment and talk to morgan. >> and she seemed genuine, like she wanted to help me. >> morgan invited the detective in and told him the same story, kevin had walked out on her and the kids and she had proof. text messages in her own phone from kevin breaking it off.

>> she had received a message from kevin that he was leaving and she showed me these text message exchanges, something to the effect of, are you kidding many he? and he said no, i'm done. i can't do this anymore. >> the detective also spoke with steve shappell, kevin's young employee who had been hanging around the apartment complex with morgan and the kids. >> he just seemed like a kid. a young kid. he was 21 years old. >> and morgan scoffed at the idea that they were anything more than friends. >> she laughed and said, no, i'm a married mother of three, i'm 34, he's 21. that's absurd. there's no affair. >> absurd is precisely what friends nicole had said had they known that. morgan had a history of cheating, sometimes with kevin's closest friends. >> she would tell me how they would have sex in her and kevin's bed when he would go

out, how they would have sex in the cars, you know, the business cars. >> i said to myself, you know, she's not right. there's something wrong with her. >> and kevin's family, by now they were sure morgan and the young landscaper were up to something. michelle confronted morgan directly. >> i said, i'm not okay with this. like he just disappeared. like, i don't believe you. like, i don't. >> adding to their worry, morgan had not let them see the three kids since kevin disappeared and they worried she might leave town. they asked the detective if she would do surveillance on the apartment but he said no. >> i said, based on the fact that we had a witness that saw him, the fact that i now know that morgan and kevin have a troubled relationship, i thought that maybe kevin really was just fed up and had enough of morgan and left. >> so the mengel family took the investigation into their own hands. brother chris decided to stake out the apartment overnight.

he brought a video camera with him. >> that's him. >> that's it? >> that's him. >> early friday morning he films steve shappell coming and going as if he now lived there, taking kevin's place. and what was strange, it looked as though steve was packing up morgan's truck. >> okay. there -- yeah, they are getting in the truck now. >> to chris, it sure looked like morgan and steve were getting ready for something. >> he has a bunch of crap with him. morgan has a bunch of stuff, too. >> he frantically called the police looking for detective maurer. >> i'm afraid his wife and the new boyfriend are making a move to leave. they are leaving. >> only, they didn't go far. chris followed them as they drove over to the landscaping business. it turns out, the detective was already there. he decided to go poke around, half expecting to run into kevin back at work. >> she gets out of the passenger side and walks directly by me. then i walk over to shappell who's still sitting in the passenger seat and he's got a dead stare straight ahead.

>> and there was something inside the truck that the detective thought was peculiar. >> the back seat was full of clothes, i could see laundry and baskets. he said morgan is going to do laundry across the street. i said, well, would you mind coming down to the station? i have a couple of questions for you. >> and in that moment as the detective turned his back on steve, something unexpected happened. something that chris mengel still on video caught. steve jumped into the driver's seat, sped out of the lot and drove away. >> morgan walks over and sits down on a step, puts her hand on her head and said, oh, my, maybe he did do something to kevin. coming up -- >> steve had said to me that he loved me and would do whatever

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it sounds so hoakie but three months before i had a horrible nightmare that something happened to kevin and that kevin was hurt.

>> michelle hopkins, kevin mengel's younger sister, was now in a waking nightmare. her brother kevin had been missing for a week and the young man who appeared to be having an affair with her sister-in-law had just fled from police. >> why did he just steal her pickup truck and flee when i asked him to come back to the police station? >> the situation suddenly looked much worse than detective david maurer had thought. he brought morgan to the station and called his partner and long-time friend, darren sedlak. >> he said, can you get in here? something's going on. i'm not sure what but shappell just stole morgan's truck and fled and we can't find him. >> we had no idea it would turn out the way that it did. >> their first priority was to find steven shappell. they tried tracking his phone but it was turned off. morgan's phone was in there and it was turned on.

she gave detectives her permission to track it. meanwhile, morgan was inside the interview room as detectives tried to figure out what steve was running from. >> do you think maybe steve hurt kevin? >> i don't know, but by his reaction today -- >> he takes your truck without your permission and, in my terms, knees the scene. >> absolutely. >> although morgan had previously denied the affair with steve, the much younger landscaper, she was now telling the detectives they were having a relationship. a result, she said, of an unfulfilling marriage. >> it was just a bad marriage. >> okay. tell us. >> a bad marriage. the yelling, the screaming, the fighting, the i can't ever do anything right. >> so tell us about your affair. how did steve treat you? >> he talked to me like i was a human being with feelings, paid attention to me. >> and she repeated yet again how kevin had walked out on her

and the kids one week earlier. >> he was leaving. um, he wanted a fresh start. >> and did you respond to him? >> i said, are you kidding many he? he told me he was not kidding. and to tell the children that he loved them. >> now, i have to ask, in the truck i saw a bunch of clothes in the back of the truck. who did they belong to? >> steve. he said he was taking his stuff, his clothes that he had accumulated at my house. >> he's been staying there? >> a few nights, yes. >> did you ever think that maybe kevin would come home and steve would be there and there would be an issue? >> no, i hadn't thought about that. >> and i said, if i get in a fight with my wife, i said, nobody's moving into my house. >> as a husband, as just a sensible person, to me that -- >> poor judgment. >> poor judgment and a bad marriage was all kevin's wife would admit to. but the family knew that morgan

had a history of deception. a strange one that went back many years. >> there's something that is innocent looking in her face that you just believed her. whatever she said, you just believed her. >> one of her biggest lies, they say, was back when morgan got pregnant before the couple was married and refused to tell the truth about it. >> we were looking at her saying, you're pregnant. and she said, i am not pregnant. >> and she would wear two girdles at a time and heavy swer sweaters and i said, morgan, did you tell kevin? and she said, no, i told him i was on birth control and it's causing my stomach to swell. kevin called me crying saying that i'm an aunt. >> was he crying tears of joy? >> i don't think so at that time. he was so scared and it caused the real fight between my brother and i because i was so very disgusted by morgan. >> so when kevin went missing,

the family had been convinced from day one that morgan was hiding something. and now the detective was, too. after hours in the interrogation room, she gave the first hint that she knew more than she was saying about her young boyfriend steve. >> steve had said to me that he loved me and would do whatever it took to have me. and then last night he said he had an uneasy feeling. he apologized to me and said it was his fault. i asked him what was his fault? and the only response i got was "the entire situation." >> do you think that steve hurt kevin? >> at this point i do. >> she had been talking all this time without a lawyer and the detective wanted to keep the conversation going, hoping she'd reveal something. and did she ever. >> we were standing in the

street, it's still extremely hot and no air conditioning because of the thunderstorm and she said, steve told me that he hit kevin in the back of the head with a shovel. and i'm like, whoa. we run back in and i turn the recording back on at that point. >> morgan, you just told me something. would you mind repeating that? >> steve hit kevin in the back of the head with a shovel. >> here was morgan laying the blame on steve, telling police he had attacked and killed kevin at the landscaping garagen on e day he supposedly left her and the kids. the detective was stunned. that earlier sighting of kevin alive and well in the town, had it been a mistake? how long had she been lying to the police? >> i'm floored. i'm like, why didn't you tell me this? i said, when your boyfriend tells you that he hit your husband in the back of the head with a shovel, you call the police. >> are you trying to protect steve? >> not at this point. >> morgan said that steve had only just revealed to her what he had done.

but the detectives suspected he wasn't getting the full story. hoping to trip her up, he asked her to write down the timeline of events for the week kevin disappeared. >> you're going to write it down? >> uh-huh. >> most of what she wrote stuck to the story but this was a strange detail. >> she writes "snapple" on one of her statements. i said, what does snapple mean? coming up -- >> i want to hear everything. you better start at the beginning because the game's over. >> a tough new interrogation and a new revelation. that single word morgan had written involved a deadly surprise. >> who handed the snapple to your husband? >> when dateline continues.

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the first break in the case of missing husband kevin mengel came out of the blue. morgan revealed that her lover steve had killed her husband in the landscaping garage. she was saying that steve had done the deed a week earlier and only admitted it to her later. she hid his secret out of fear. >> i didn't know if he was going to whack me up the side of the head with the shovel. if he did and you guys showed up and flipped out. >> you're telling me that he hit the father of your children in the back of the head with a shovel and you don't tell me that information? >> a bit of shock. >> i personally feel it's because you had some role in

this. >> i had no role in this. >> but detective maurer did not believe her. he looked at the timeline she had written out puzzling over that one word. snapple. why did she write that down? the detective took a break, went upstairs to speak with his partner, detective sedlak. >> and it was sort of like a mental slip and then i asked him if he minded if i had a shot. i wanted the chance to talk to her myself. >> and so the detective decided to play good cop, bad cop with morgan. >> i want to hear everything. and you better start at the beginning because the game's over. >> and now morgan was about to offer a new piece to the puzzle. a truly shocking one. it had started as a joke, she said, the two lovers imagining kevin out of the picture. >> joking around, we could take kevin out, yeah, right. >> what would happen, they wondered, if they put something in his favorite drink.

>> he put nicotine, straight nicotine in a snapple that he bought. >> following a recipe he found online, he put chewing tobacco into a toxic substance called liquid nicotine. he then slipped it into kevin's n snapple. >> who handed the snapple to your husband? >> i did. >> and then what? >> i left and got my kids off to school. >> but morgan insisted she never expected any real harm to come to kevin, never expected steve would take it as far as he did. and besides, it wasn't the poison that killed kevin but the blows to the head, which steve had done alone inside the landscaping garage. >> i wasn't being serious. apparently it did turn into a serious conversation on his end. and, yes, i did hand kevin the

snapple bottle with nicotine in it. after that, i was not involved. >> you guys killed someone. and you expect me to believe that you didn't talk about it? >> no. i didn't want to talk about it. i looked at my kids and felt terrible. >> so terrible that you made up text messages to his family members about him calling you and texting you. >> i did not do that. >> who did? >> steve did that. >> it was steve, she said, who used kevin's phone to send messages to his family pretending kevin was still alive. and steve and steve alone who had buried kevin in some woods a few towns over. >> and where did he tell you that he took kevin? >> behind a high school, there was a development being built. >> the interrogation had turned deadly serious. but the detectives thought that morgan's demeanor was odd. when detective maurer asked if he could take pictures for evidence, he says she didn't

look like someone facing a potential charge of murder. >> and while i'm talking these pictures, she's actually smiling for the camera, which is weird. >> and in the middle of his bad cop interrogation, detective sedlak says it was almost as if she was flirting with him. >> my questioning was not nice, by any means, and i just couldn't believe that she was smiling and looking up at me. >> is this funny? >> no. am i laughing? >> you just smiled. >> no, i didn't. >> the detectives felt they had enough. they issued a warrant for steve shappell, who was still on the lam. and morgan -- >> we handcuffed her inside the interview room and told her that she was under arrest for the murder of kevin mengel jr. >> they sent a police officer to talk to kevin's father. >> he said that we believe that your son has been murdered.

it was not easy to sit and listen to. >> kevin's three children were spending the day at his sister michelle's house when she learned that kevin was not coming back. >> kevin's kids came in and they just came up and they just started hugging me and they said, what's wrong? i think they knew. >> michelle had known all along, she says, in her gut that kevin was dead. but how it happened, michelle could not believe what police were telling them. she remembered steve shappell as that scrawny unassuming guy who worked for kevin mowing lawns. in fact, he had done some work on michelle's yard just a few weeks earlier. michelle felt badly when he told her he had just had his wisdom teeth out. >> i was so worried about him for the two days that he was there and to think what he did to my brother -- >> and her sister-in-law, it

felt impossible to take that in. >> when i saw her, i didn't even rec fiz her. she just had a different look about her. she's been in my life for 15 years and i didn't even know who she was. >> the next morning, detectives recovered kevin's body buried in a shallow grave right where morgan said it would be and the following day steve shappell was picked up nearly 2,000 miles away in colorado. >> i still can't imagine him doing it. i can imagine morgan doing it. i don't know what they were thinking. >> figuring out what they were thinking was now the job of the county prosecutor. and it would prove to be more complicated than expected. >> did she say you needed to go dig a hole? >> morgan had pointed the finger at steve, but now he was back and about to tell a very different version of events. >> on the day of the murder, she's texting him, has the poisoned work yet and when it's not working fast enough she says, couldn't you just pick up a shovel?

>> the truth? well, that takes us right back to where our story began. the tale of the texts has another chapter to come. coming up -- who was the mastermind? morgan? >> she used him as a pawn to do her actions. >> or steve? >> is he a cold-blooded killer. >> a few surprises were still in store. >> we were like, holy smokes. and coming up next friday on "dateline," they were high school sweethearts raising five strapping sons. >> for them it was all about family. >> yeah, always. >> and then that terrible night. >> she's got blood everywhere. everywhere. >> a mother murdered. tips pouring in. reports of strangers lurking and footprints out behind the house. >> somebody's out there. >> but when an arrest was finally made, the suspect was no stranger. >> he couldn't believe it. like, are you kidding many sne. >> did investigators rush to judgment?

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morgan mengel and her young lover steve shappell were both sitting in jail for the murder of morgan's husband kevin. morgan had confessed to playing a small part in the crime, helping steve shappell come up with the plan to spike her husband's snapple iced tea with poison, only it was a joke, she said, that was taken too far. >> what were your first impressions of her? >> very good. i peemean, the allegation compa to the person that i was speaking to did not seem to fit. >> morgan's attorney, jack mcmahon, said that she wasn't at

the crime scene when kevin was killed ahad no convincing motive for wanting her husband dead. >> financially she was way worse off with her husband's death than she would have been with him alive because he was the life blood of the company and there was no life insurance. >> you think she had some musing about it, i wish my husband wasn't around and i wish someone would take care of it? >> i think morgan was walking around with dynamite, so to speak, and stephen shappell was the mass that lit that dynamite and exploded it but that person that took action was shappell. he is a cold-blooded killer. >> a cold-blooded killer? he hardly even looked like one when police picked him up in denver and got him into the interrogation room. he was meek. his voice was quiet and shaking with fear. district attorney jack carmody. >> he said he was in love with this woman and this was the way to get her forever.

>> he said that morgan was not kidding when she said she wanted him dead. and steve said after the murder, far from being scared, morgan was grateful. >> she kissed me. she came back with water and began, like, rinsing off the area where it happened. >> which is why the garage looked so clean when employees arrived for work that monday morning after kevin's so-called departure. >> she walks into the garage, steps over her dead husband, kisses shappell, tells him to get a tarp and said let's get to work cleaning the scene. >> so now they were pointing fingers at each other about who really planned the murder and the d.a. believed steve. he offered him a lesser charge of murder to testify against morgan and charge morgan with premeditated murder, a mandatory life sentence. >> i think she found the most gullible person she could. she used him as a pawn to do her actions.

he held the shovel but morgan held the strings. >> so you think morgan was in charge of this operation? >> 100% i believe that. morgan had a way with men. she just did. she had a way with men and i think the same way that she had my brother, you know, under her spell, she had this kid as well. >> and the d.a. says it was morgan herself who had been sending those fake text messages to kevin's family after the murder, not steve. cell phone tracking records proved it. >> she's texting kevin's family assuring them that he's okay, he just wants to be left alone. she's the most evil woman i have dealt with. >> morgan mengel went on trial in late january 2012, a year and a half after kevin mengel had been murdered. but in addition to steve shappell waiting in the wings to testify, the d.a. had something else, something extremely rare in a murder trial. a play-by-play of the crime,

courtesy of text messages between morgan and steve as it happened. >> we were like, holy smokes, there it is. it's right there. >> the detectives had discovered the trove of messages during their investigation when they pulled morgan's phone records looking for steve. >> we few the exact time of death, we knew how it happened. and so we were floored. >> the texts are chilling. four hours before the murder, morgan texted steve. we ready, she types? steve responds, yep, at the shop now. then a half hour before the murder, morgan asks steve about the poison snapple. he drinking it, she asks? steve writes back, yeah, kind of. really just waiting for him to bend over. i have a shovel in my hand. ha, ha. morgan's response, nice, babe. steve doesn't reply. morgan writes, you backing out? >> there's a gap there where nothing happens and she then gives him the final taunt, you backing out?

and when she says that, he texts back, it's done. get here now. >> these text messages don't even seem real. they just don't seem real. >> as incriminating as those messages sounded, morgan's defense was ready to press her case in court claiming she was no murderous mastermind. >> i'm not so sure even to this day that she had a fully formed belief that steve shappell was going to actually do this. >> but the defense never got a chance. a few days into the trial, a police officer said something on the stand. hearsay that could prejudice the jury and the judge sent everyone home. >> chester county judge declares a mistrial in a love triangle murder case. >> for kevin's family, the delay was torture. more waiting for answers to questions they never wanted to ask. >> i wanted to know if he knew it was happening. i wanted to know if he begged. >> why did you want to know? >> kevin was so sweet and kind.

and i know he must have been so, so scared. >> the story of those final moments could only be told by steve shappell. but even from jail as they awaited their fates, morgan was trying to keep him quiet. she wrote him a letter saying she had given birth to his twins. >> so her game plan was, if he thinks we have kids together, he's not going to rat me out? >> yes. she would always ask him that in letters, have you figured out who has a better chance to get out of here? i need you to do that for me so we can raise our children. >> except, of course, it was another lie. another manipulation. this past february, the prosecution and defense were back at the chester county courthouse for morgan mengel's retrial. steve was set to testify but, then, another surprise. the day the testimony was set to begin, morgan stopped the trial from happening and changed her plea. she admitted to first-degree

premeditated murder. even her own attorney was stunned. >> i believe morgan saw the handwriting on the wall. she realizes that whatever actions she took resulted in his death and resulted in shappell killing him. >> steve was sentenced to 40 to 80 years. and morgan, life without parole. for the mengel family now raising kevin and morgan's children, there is finally some justice, they say, in knowing morgan will remain behind bars forever. >> i want her to be in jail for the rest of her life. i want her to know that i'm going to be there when her daughter walks down the aisle. i'm going to be there when her daughter has a baby. i'm going to be there with her sons when they meet their wives and graduate from high school. i'm going to get to see all of that. and she is not. she's in hell and she's going to live this way for the rest of

her life. >> that's all for now. i'm lester holt. thanks for joining us. >> so how did you spend 2013? did you waste hours obsessing over kim kardashian's baby? come on, guys. posting endless selfies of all your friends? or did you and your buddies make your own "harlem shake" video? well, now it's time to take a look back at all the glorious ways we squandered the last 12 months. this is "what we wasted our year mmm -- cronuts. ♪ [ cheers and applause ]3 f1 i'm willie geist, and this is "what we wasted our year on."