. >> nique leili, a corporate executive who made time for romance and her three daughters. >> she was the best mom. >> then she disappeared. dozens joined the search. >> we need nique to come home. >> then, they found her. [ screaming ] >> you can't! you can't, baby. >> launching a mystery that would divide this family. >> i suspected him from the beginning. >> one daughter thought her stepdad, matt, did it. the others said no way. and matt, he had a theory all his own. >> this is not the first time she's run away, okay? >> had nique taken off and found trouble? >> now you're thinking someone gave her a date rape drug. >> that's a possibility. >> the trail would lead to this house of cameras. >> there is a big server tower that would indicate a large amount of data being stored. >> what they discovered, thousands of hours of tape. >> let me out of this room. >> it's absolutely a torture to listen to. >> and would reveal one shattering truth. >> i got down on my knees and just started crying. >> i'm lester holt and this is "dateline." here is dennis murphy with "the house on sydney's c

you will hear the voices of nique leili and the defendant in this case arguing. >> nique's murder, she matt leili's final act of control. >> i think they got into an argument, that he wanted to have sex, that he drugs her, that he has his way. she is loud, she is not able to resist as much as it progresses, that he silences her. that he strangles her, he sits on her, he asphyxiates her to where she can't breathe. >> not meaning to, maybe. >> i think he meant to. i think he had it. i think he knew she was leaving him. she made it clear she was done. >> raise your right hand, place. >> the state's first witness was nique's oldest daughter alex. >> they would be arguing. he would end up locking her in a bathroom. she had been shoved down stairs. there were several nights that i would lay up at night and listen to her say, please get off of me. get off of me. you're hurting me. >> next, nique's sister amy told the jury about the constant monitoring at the leili house. >> we knew that he would record phone conversations that came into or out of the house. >> were you aware at any time wheth

. >> nique leili, a corporate executive who made time for romance and her three daughters. >> she washe best mom. >> then she disappeared. dozens joined the search. >> we need nique to come home. >> then, they found her. [ screaming ] >> you can't! you can't, baby. >> launching a mystery that would divide this family. >> i suspected him from the beginning. >> one daughter thought her stepdad, mt,