this is "nightline." >> tonight, finding kelsie. a young pregnant woman gone without a trace. >> i called doug, her dad, and said, you know, something is wrong. >> her former boyfriend under suspicion. >> can i speak to a lawyer, please? >> piecing together the clues. >> do we suspect foul play, yes. have we come up with a body, no. >> even with no weapon and no crime scene, the prosecutor's vow. >> i think i owe it to the family, i think i owe it to kelsie, to go forward and try this case. >> one mother's eight-year crusade for justice. want to brain better? unlike ordinary memory supplements— neuriva has clinically proven ingredients that fuel 5 indicators

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goes before you. essentially disappear without a trace i think is kind of a counterintuitive thought for people to have. >> reporter: it's the story of 21-year-old kelsie shelling who went missing in 2013, and her mother, laura saxon's eight-year-long search for justice. >> her family is pleading for your help. >> we are doing everything in our power to find our missing loved one. >> reporter: kelsie grew up in the farm town of holyoke, colorado. it's a carefree, happy childhood shared with brother colby. >> she's been a firecracker. >> reporter: as kelsie enters her teen years, the family is rocked when doug and laura divorce. >> the split of our parents had an impact on both of us. >> she ended up in the hospital for several days, and it was pretty scary. >> she was on an anti-depressant pill and she ended up taking three of them. >> i thought we were going to

lose her at that point. >> reporter: kelsie gets her life in order, moving on to northeastern junior college in sterling, colorado. >> she wanted to get a degree in psychology. i think in her heart she wanted to work with children. >> reporter: for a while, carefree kelsie is back. then she meets donte lucas. >> it was a big deal that she was dating donte. he was part of the basketball team. they were kind of the popular kids and everything. >> when did you first meet him? >> i never met him. i saw him play basketball a couple times. he was not committed to her by any means. >> he would play with her heart. i could definitely see some bubbliness feeding out as he broke her spirit. >> reporter: donte and kelsie date on and off. after leaving school kelsie moves to denver where she lands a job.

donte moves back to pueblo. when did she start going out with donte again? >> over the holidays, november, december. he would stay with her, then go back to pueblo sometimes. >> were you worried he would come back and what that would do to her? >> absolutely. she didn't want that to happen because she knew the kind of person she became when she was with him. >> reporter: around the holidays kelsie has a surprise for her family, she's pregnant. >> i told her, i will support you. it's going to be okay. she was happy. >> did she tell you anything about donte's reaction? >> she said he was mad, very angry. >> reporter: on february 3rd, 2013, donte asks kelsie to visit him in pueblo. she says no. they continue to fight over text. >> just before 3:00 a.m., kelsie texted donte, you don't have to be in a relationship with me, you don't have to marry me, you don't have to have a happy family with me, you don't have an obligation with me, you're good, don't worry, good night.

lucas' response, i know all of that, thanks for stating that for me. >> reporter: the next day, kelsie visits the doctor who confirms her pregnancy. >> what did you think when you saw the baby? >> i was happy. >> that morning, kelsie told donte she had finished her appointment, due date september 13th. lucas' response was cool. he asked her to skip work and come to pueblo. she texted, i'm not going to come get you so we can fight. he texted, i don't want to fight, i want to give you this. she writes back, give me what? he says, wait and see for yourself, you probably wouldn't believe me if i told you anyway, you can see for yourself. >> reporter: kelsie decides to drive to pueblo after work that night. she and donte plan to meet the a local walmart. she arrives at 10:20 p.m.

after waiting for almost an hour, donte is still not there. the two decide to meet near donte's grandmother's home where he was staying at the time. >> the last confirmed message from kelsie was 11:18, where are you, i've been here over an hour just waiting. >> reporter: the next day, kelsie doesn't show up for work. over the next several days, family and friends grow worried. kelsie's not answering phone calls. they say her text messages just don't sound like her. >> i'd called doug, her dad, and said, something is wrong. >> reporter: kelsie's family drives to her apartment in denver, but there was no sign of her. they eventually call the police, who reach out to donte. >> he was telling me that he had seen her and talked with her and spent time with her more recently than any of her family members, friend. i did have a sinking feeling in my stomach. >> reporter: police turn the case over to the pueblo police.

when donte is brought in for questioning, he denies a serious relationship with kelsie. >> came to pueblo, we were talking. >> reporter: donte says kelsie slept in her car in pueblo, then he met her the next morning and they stopped at walmart before she headed back to denver. >> she went to go get some snacks, something to eat, she was hungry. came back, we ended up talking. she ended up telling me to get out of the car at walmart, she didn't want to take me home. i left the walmart, started walking home. my mom came and got me. >> reporter: surveillance video shows just donte getting out of kelsie's car. >> the morning of february 6th, this unknown man is seen walking to kelsie shelling's car and is seen driving away with the car. we have no idea who that person was in that video.

>> who do you think that someone was that came back and drove that car away? >> there's similarities to donte, but it's nothing that we can say, that is the person that drove it away. >> reporter: february 14, kelsie's car is found in pueblo, but no kelsie. >> police start working backwards, going through surveillance video. what they find is surprising. less than 12 hours after she would have arrived in pueblo, surveillance video shows donte in her car at an atm in pueblo, he's driving, he takes $400 out of kelsie's bank account. >> reporter: donte is brought in for a second time by pueblo police. >> when you dropped her off at walmart, where were you parked at? >> apparently you guys know, so i don't understand -- like i told you, i don't -- that's all i can say about it. >> dropped off when was that again? >> can i speak to a lawyer, please? >> reporter: once he requests a

lawyer, all questions come to a halt. >> how did you read that? >> as the possibility that he knows something. >> reporter: donte's arrested on felony identity theft but the charges are later dropped after investigators find out kelsie occasionally gave him permission to use her bank card. >> he's released. he's living his life. >> do we suspect foul play? yes. have we come up with a body? no. donte is a person of interest in the fact that she's missing. >> reporter: police speak to his mother about february 5th, the day donte is seen on surveillance camera parking kelsie's car at walmart. >> did you pick donte up? >> i did pick my son up. >> reporter: she gives donte an al buy for february 6 when the unknown man is seen moving kelsie's car from the walmart. >> no way that was him. no way. he was at home. i know my son. he's not capable of hurting anybody.

>> without a body or any direct evidence that tells us something happened to her, to a homicide, you know -- it may happen one day, but right now, we haven't had any evidence to reclassify it. >> reporter: kelsie's family grows frustrated with the investigation. laura launching search party after search party. >> that turned into justice walks around the pueblo police department and the district attorney's office. >> we appreciate you all so much. your support keeps us going. coming up next -- >> it was a homicide investigation, in our eyes. ♪ ♪ ♪ why do you build me up, build me up... ♪ ♪ buttercup... ♪ ♪ baby just to let me down! ♪ ♪ let me down! ♪ ♪ and mess me around... ♪

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♪ in the spring of 2016, there are a couple of key developments in kelsie's case. in may, "20/20" airs its first episode about the case. at the same time, law enforcement has major news. the colorado bureau of investigation is going to join the case. >> i was like, oh my god, this is awesome. >> reporter: pueblo police department commander bravo and kevin torres change from it a missing persons case to a criminal investigation. >> it was a homicide investigation in our eyes so i immediately started working on setting a plan into motion how we wanted to proceed. >> reporter: then in late 2017, a pueblo mantels police donte had stolen $1,000 from him, giving them a reason to arrest donte. but donte was on his way to the airport to catch a flight to tucson. >> the concern was that he may

take other efforts to meet friends in mexico. donte was within 20 minutes of getting on a plane for tucson, arizona, when he was arrested. >> reporter: during questioning, donte admits it was him on that walmart surveillance video. that admission plus the text messages, cell phone records, and surveillance video, is enough for prosecutors to move forward. >> a major development, the ex-boyfriend of a pregnant denver woman who went missing four years ago faces charges of first-degree murder. >> how were you thinking as his trial approached? are you thinking justice will be done? >> i put a lot of things on hold because i just was, you know, sure it was going to happen. you know, wanted to be ready to go. >> reporter: michelle and husband kyle lead the prosecution. they were hired by her father, jeff, the pueblo county district attorney. >> did i think it was going to be a tough case? absolutely. and we well may not win it.

but i owe it to the family. i think i owe it to kelsie to try this case. >> these were two people in a relationship. kelsie shelling became pregnant. donte lucas didn't want to have a baby. and he made sure that didn't happen. >> for the prosecutors, their goal was to show that those text essages showed intent, showed that donte lucas consistently lied, not only to investigators, but to laura saxton herself. >> we know that's his phone, he admitted to those text messages, we know that's his thoughts and feelings about it. that's direct evidence. >> the movements of their phones pinging off cell phone towers in pueblo on the night of february 4th and february 5th. >> reporter: the prosecution has a few surprise witnesses, including donte's own mother. >> the one important thing that i've mentioned, she confirmed

that donte was the last person left alone with kelsie. >> reporter: some of kelsie's friends testified, pointing towards possible domestic abuse by donte. >> the prosecution and even the defense made it clear that donte was using kelsie for a number of things. for her money. donte used kelsie for her apartment in denver. donte used kelsie for her car. and his argument was, she lets me do it. >> reporter: on the last day of its case, the prosecution plays the interrogation video of donte admitting that he was the figure in the surveillance video picking unclesy's car in the walmart parking lot. >> the clip that i played at the beginning of my closing was his phrase to detectives, "i lied from the jump, i moved the car." i wanted the jury to hear the defendant in his own words say,

i lied. >> reporter: with no body, no weapon, and no crime scene, the defense presents the case as a missing persons case. >> you didn't have the forensic evidence, it seemed like you were really relying on circumstantial evidence and these other witnesses. that's pretty straightforward. either you believe them or you don't. >> reporter: the defense also tried to paint kelsie as a pill-popping party girl. >>ers this no single person, other than the defendant in 2017, who's saying she was into drugs and she was a party girl. >> the defense didn't call a single witness to the stand. the defense immediately rested their case. and it was just another moment where your jaw hit the floor. >> the burden of proof is on the government. it's simply messaging in a very strong way to the jury, they haven't done it, it's not guilty. so it's a strong message. >> reporter: the last thing

anyone expected was to get a verdict the same day the trial ended. >> i was prepared to camp out at the courthouse as long as i had to. we were totally unprepared for when they came and told us the verdict was in. i think we all were just like, oh my god. >> reporter: the jury takeso fi guilty of first-degree murder. he's sentenced to life in prison without parole. >> when you hear the verdict, tell me how you're feeling. >> the words came out way too slow. like i feel like the judge was talking in slo-mo, even though he wasn't. i mean, i was just like, every word it's like, okay, okay, spit it out, please. then he finally got to, you know, guilty of first degree. and -- i think that was the first breath like i had taken in a long time. >> reporter: laura may have found justice for her daughter's murder. but she didn't find her

daughter. >> we're very, very thankful for this outcome. but in the end, i didn't get kelsie back. and that's what i wanted more than anything. so i feel like i didn't do something, i didn't push hard enough on something, or i didn't look enough on something, to bring her home. >> it turns out that prosecutors did present troubling evidence from the night kelsie disappeared. >> we received information from the pueblo landfill ■thatthere was some video evidence of a vehicle being there. you couldn't see what kind of vehicle. you couldn't tell who was in the car. their lock to their front gate into the dump had been tampered with. the cell phone records of pings were all out in that area. so, you know, we suspected that's what happened. >> who wants that for their

child, to be the final resting place? no one i'm never going to recover. without getting her back. so i still have nowhere to go to take her flowers, to go sit and talk with her, take her balloons on her birthday. you know. go to see her on the holidays >> you want her to be remembered. >> a little girl with a really big heart, a really big smile, a really big laugh. beautiful eyes. i miss all the things that we didn't get to do togethe

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that's "nightline" for this evening. watch our full episodes on hulu. see you right back here same time next week. thanks for the company, america. hope you have a safe weekend. good night. want to save hundreds on your wireless bill? with xfinity mobile, you can. how about saving hundreds on the new samsung galaxy s21 ultra 5g? you can do that too.