Dateline | April 03, 2013
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>>> the first break in the case of missing husband kevin mengel morgan , the wife, under questioning by police, revealed that her lover steve had killed her husband in the landscaping garage. she was saying 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 upside the back of the head with a shovel if i did and you guys showed up and he flipped out.
>> reporter: the man you're having a relationship with tells you that he hit your husband, 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.
>> reporter: but detective maurer did not believe her. he looked over the timeline she'd 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 a chance to talk to her myself.
>> reporter: and so the dktd decided to play good cop, bad cop , with morgan .
>> i want to hear everything. you better start at the beginning because the game's over.
>> reporter: 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 how we could take kevin out. yeah, right.
>> reporter: what would happen, they wondered, if they put something in his favorite drink?
>> he put nicotine, straight nicotine in a snapple .
>> reporter: following a recipe he found online steve cooked up some chewing tobacco into a toxic substance called liquid nicotine. he then slipped the poison into kevin 's snapple .
>> and then who handed the snapple to your husband?
>> it was on the truck -- i did.
>> reporter: did you say anything to your husband like, that drink's for you?
>> reporter: and then what?
>> i left and got my kids off to school.
>> reporter: but morgan insisted she never expected my 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.
>> reporter: 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.
>> reporter: 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.
>> while i'm taking these pictures she's actually smiling for the camera, which is weird.
>> reporter: 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.
>> reporter: 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 of the interview room and told her she was under arrest for the murder of kevin mengel jr.
>> reporter: 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.
>> reporter: 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. they're like, what's wrong? they just -- i think they knew.
>> reporter: 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'd done some work on michelle 's yard just a few weeks earlier. michelle felt badly when he told her he 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.
>> reporter: and her sister-in-law, it felt impossible to take that in.
>> when i saw her mug shot , i didn't even recognize 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 he was.
>> reporter: the next morning detectives recovered kevin 's body buried in a shallow grave behind that high school 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.
>> reporter: figuring out what they were thinking was now the job of the county prosecutor, and it would prove to be morgue co -- more complicated. 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 poison worked yet? and when it's not working fast enough, she says, can you just pick up a shovel.
>> reporter: the truth? well, that takes us right back to where our story began. the tale of the texts has another chapter to come.