i've been in my life. i'm happy as a clam, to be honest. i really am." in 2022, a federal judge concluded that hinckley's mental illness was in full remission and granted his unconditional release. it was a new chapter in the life of john w. hinckley jr. who four decades after shooting an american president appeared at peace with his past. that's all for this edition of "dateline." i'm andrea canning. thank you for watching. i'm andrea canning, and this is "dateline." someone at a park at 3:00 am. i think she knew the second she got in his car that something was wrong. andrea canning (voiceover): a college student disappears.

andrea canning (voiceover): a secret life uncovered. she was on a dating site looking for sugar daddies. going into it blindly is not something i would recommend. andrea canning (voiceover): chilling details revealed. is this guy dodging us? he kind of selected her as his victim. correct. towards the bottom of the dig site, there was a damaged iphone. it looked like maybe clothing. it was just a sinking feeling, really. i just replay this one night i had with her, and i just want to grab her and say, don't do it. don't go. hello, and welcome to "dateline." college student mackenzie lueck was diving into adulthood, eager to find her path. her family and friends knew her as fun, responsible,

and always careful. then, one night, mackenzie vanished. a trail of electronic clues helped investigators retrace her steps and exposed a dark underworld where evil was hiding behind webs of lies. here's keith morrison with "the waiting car." keith morrison (voiceover): our minds have a curious way of deceiving us. we sense something off, something wrong, even terrible, and yet something in the brain wants to believe the worst didn't happen. kennedy stoner knows that feeling well. i was kind of pushing away from my gut instinct. i'm not really sure why. i never imagined this ever happening to one of my friends. i wouldn't think you'd want to imagine it, right? no, or anyone that i know or--

so my mind didn't go there. keith morrison (voiceover): so she told herself it would be fine, as she reached out from her home here in salt lake city, utah, messages to her friend, mackenzie lueck. kennedy stoner: i saw that she wasn't opening my snapchats. and i had texted her, and i didn't get a text back. and this is stupid, but i was kind of wondering if she was mad at me for something. keith morrison (voiceover): the mind wants a simple explanation. after all, she knew her best friend was grieving. mackenzie's grandmother had recently passed away in california. i know she was heartbroken over that. and so was the rest of her family because they're all very close. and she went to the funeral. she did. she left utah. she went to the funeral. so i was thinking maybe she just took a few days off social media or something. keith morrison (voiceover): mackenzie's parents, though, hadn't heard from her either. after three days of escalating fear, mackenzie's dad made that most dreadful phone

call to the salt lake city police department. and i've been trying keith morrison (voiceover): the story mackenzie's dad told was this. on the night of sunday, june 16, 2019, mackenzie had boarded a flight from los angeles back to utah, arriving in salt lake city around 1:35 am monday. at 2:01 am, she texted her mom to say she landed safely. after that, three days of silence. two patrol officers went straight away to mackenzie's townhouse. her car was in the driveway. that was a good sign. [knocking] repeated knocks at the door, however, went unanswered.

peering through a window, the officer saw nothing. not a soul around. he called mackenzie's dad to report the news. and next, the officers phoned mackenzie's friends, boss, and professors. none of them had seen her-- all reasons why, by the end of this unsettling day, mackenzie's case was referred to a place that sounded very serious, indeed-- the salt lake city police department's homicide squad. we get a lot of missing persons cases in salt lake city. keith morrison (voiceover): lieutenant todd mitchell was the unit's chief detective. so i tried my best to sift through those and find the ones that kind of raised the hair on the back of your neck, for lack of a better term. and this raised the hair on the back of my neck. so that's why i decided, yeah, we need to take action now and at least start an initial investigation into it. keith morrison (voiceover): truth be told, most reports are easily resolved.

the missing person may have simply lost their phone or just decided to take a break from some family drama. but that didn't appear to be the case with mackenzie. the relationship she had with her mom and dad would be the envy of most parents. they were always contacting each other. they'd send little silly texts back and forth on a daily basis. keith morrison (voiceover): detectives nate wiley and tiffany sayes led the missing persons investigation, even though their specialty was murder. i mean, in a usual homicide investigation, we start-- there's a dead body. we are starting with something. we have a victim, and we're moving backwards. in this case, we started with nothing. keith morrison (voiceover): first action sayes and wiley took was to pull the salt lake city airport surveillance camera footage from the night of mackenzie's disappearance. and sure enough, there she was. so it was nothing out of the ordinary. we were able to see her come off the the terminal, and we followed or all the way down to the baggage claim to where she picked up her luggage.

seemed perfectly normal, fine, casual? yes, nothing out of the ordinary that we could see at all. keith morrison (voiceover): the last clip shows mackenzie, like so many other passengers, casually getting into a car outside baggage claim. but the identity of the driver a mystery. news of this police investigation quickly spread among mackenzie's friends. the second that i heard about that, my stomach dropped. keith morrison (voiceover): so kennedy launched her own investigation. i went on facebook. i dropped pictures of us together, and i said she's missing. like, if you know anything, reach out to me. reach out, please. i thought she was still in california until i saw kennedy's message on facebook. keith morrison (voiceover): ashley fine, another of mackenzie's college friends, put up her own facebook post. and i tagged her in it. and because i tagged her facebook,

some of her other family members reached out to me immediately. what family members? some of her distant cousins. ok. one who lives here in utah, and we started talking and messaging. and i said, you know, i have a feeling that she took a lyft share. i feel really strong that she did that. so you're worried that maybe something happened in that car. definitely. keith morrison (voiceover): on their own, ashely and this cousin called lyft and uber to see if either one of them had picked up mackenzie at the airport. and that's really when this began because somehow they let it slip, lyft did, that she got in a lyft that night. what did you do at that point? we contacted law enforcement about the lyft. keith morrison (voiceover): a big break for sayes and wiley because it gave them probable cause to serve lyft with a search warrant. and find out where her destination was, where she was dropped off, what time she was picked up.

where did she go? so we were able to get the destination from the airport all the way up to a north salt lake address. and she was dropped off at hatch park up in north salt lake just before 3:00 am. keith morrison (voiceover): a park at 3:00 am? why would mackenzie come here? and just as important, why would a driver leave a young woman alone, burdened with luggage at a park in the middle of the night? who would do such a thing? it was detective sayes' job to track down the driver, who, she discovered, was not so easy to find. we were like, is this guy dodging us? andrea canning (voiceover): coming up, mackenzie's friends have a terrifying theory about why she's missing. i assumed that the lyft driver abducted her. andrea canning (voiceover): and here's one reason why. her last text message that we recovered was at 2:58 prior to her arriving

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she takes robitussin. so she can have those one-on-ones again. hey, jim... can we talk about casual fridays? for sure. what's up? get fast powerful cough relief with robitussin and find your voice. ♪robitussin♪ to my son, i've never been the cool dad. i always wanted to know what he's up to online. but with tiktok's privacy settings being on by default for teens under 16, accounts are set to private. he cannot send or receive dm's, and only his friends can comment. so he can post away, and i've got one less thing, to worry about. so, dad, how old do you have to be to get a tattoo? uh, um. teen safety settings on by default. ♪♪ keith morrison (voiceover):ngs before mackenzie lueckault. disappeared in june 2019, a disturbing story had gone national-- several stories, actually-- about women being assaulted while using lyft or uber.

at least 14 women have now filed a lawsuit against the rideshare giant. keith morrison (voiceover): and, perhaps, no surprise, mackenzie's friend ashley fine imagined something like that or worse. i assumed that the lyft driver abducted her, or maybe they were in a car accident and had their car driven off the road. keith morrison (voiceover): the detectives thought that was a possibility, too, so they wanted very much to find that elusive lyft driver who gave mackenzie a ride the night she vanished. we wanted to know if he was, in fact, going to be a suspect or not. keith morrison (voiceover): he was, though, nowhere to be found. just as odd, mackenzie's phone, the detectives learned, was turned off just as her lyft ride came to an end. her last text message that we recovered was at 2:58, prior to her arriving at the hatch park location. and that was the last activity ever we had on her phone.

keith morrison (voiceover): on the morning of saturday, june 22, six days after mackenzie went missing, detective tiffany sayes finally tracked down mackenzie's lyft driver. he says, there wasn't a lot of conversation going on in the car. he did recall her being on her phone, but he didn't know who she was talking to. was he fully cooperative? did he seem-- - oh, yes, definitely. --that he wanted to help you? he did. he didn't seem like he had anything to do with this at all. keith morrison (voiceover): because he had an alibi, a very good one, actually. as soon as he dropped mackenzie off, surveillance footage at a nearby intersection captured him leaving to pick up another fare, the date, time, and location all confirmed by the tracking software on his lyft app. and he continued that through the night, and so-- so you could eliminate him pretty easily based on the fact he was elsewhere. very quickly, yes. she was smiling. she was in good spirits.

keith morrison (voiceover): mackenzie's lyft driver, heath canada, told police, and, later, us, he remembered the weird drop-off location. even mackenzie commented on that, he said. saying how it was odd to be dropped off in the middle of the night at a park. keith morrison (voiceover): canada, though, said he wasn't too worried because someone with a car was there waiting for mackenzie. i unloaded her luggage, said goodbye, and drove away. keith morrison (voiceover): so who was that someone in the waiting car? the detectives were hoping they could identify him or her through mackenzie's phone records. and she had been texting a number with a 206 area code right up to the point her phone went dead. so we were able to actually take that number and run it through our little databases, and it came back as absolutely nothing, didn't come back to anybody.

keith morrison (voiceover): had to be some type of burner phone, they thought. so whoever that was did not want anyone to know, anyone in any official capacity, to know who it was. yeah, it was pretty obvious at that point. keith morrison (voiceover): but according to the lyft driver, whoever met mackenzie at the park made no effort to conceal their identity from her-- to the contrary. they seemed to know each other really well because i think all i heard was, how are you doing? how was your trip? just kind of basic greetings. the situation seemed very safe. she obviously knew the person that she was getting into the car with. keith morrison (voiceover): that mackenzie had caught a ride with someone she knew was both good and bad news. the good news, of course, was it meant maybe mackenzie just went off with a friend somewhere. the bad news? because there was now no proof of a crime, the detectives had lost their power to get any additional search warrants.

we had lost our what we call probable cause that a crime had been committed. and so-- just like that because-- just like that. --supposedly-- just because of what the lyft driver said, suddenly, you can't be getting warrants for things. correct. and so that was a hard part, and it really slowed down the investigation at that point because we didn't have a crime to attach to it. it was still now just a missing persons investigation. keith morrison (voiceover): without a warrant, the detectives were blocked from getting detailed phone records, which, theoretically, would have shown who mackenzie was texting. so who was this friend mackenzie met at the park, and where did they go? investigators are about to uncover fresh clues that deepen this mystery, but also give mackenzie's loved ones a glimmer of hope. andrea canning (voiceover): coming up, one place mackenzie wasn't missing was on social media. different people stating, hey, i'm looking at her site right now. it's showing that she's actively online.

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it made no sense, thought her friend, ashley fine. i can't even believe she would meet someone at a park at 3:00 am. it's just so unlike her. it is? so unlike her. keith morrison (voiceover): because mackenzie, like most of her sorority sisters, had talked a lot about safety. i mean, i've been out with her a lot of times. and she's always been extremely safe. she's texted me after going out at night and said, hey, did you make it home? are you ok? you would exchange things just to keep each other safe? mm-hmm, yes. keith morrison (voiceover): ashley had met mackenzie almost four years earlier. she was a little bit shyer than people would think she would be. but once you got to know her, she had a big personality. she could make anyone laugh. keith morrison (voiceover): kennedy stoner also met mackenzie in college. her family doesn't live here, so she was on her own here. so she had a job. she was going to school. she's, like, checking off everything that a responsible adult would have on their checklist,

i guess. keith morrison (voiceover): mackenzie grew up near los angeles, el segundo, california. and she was raised in the church of latter day saints, but when she came to the university of utah to study kinesiology, according to ashley, mackenzie didn't exactly remain devout. i know she was registered here at a ward in salt lake city, but i heard that she was never active, and that makes sense to me because i think she wanted to find her own path. you saw her changing in recent times, didn't you? mm-hmm. in what ways? i think she was trying to almost gain confidence and security in herself. she'd always write herself, like, notes saying how she wanted to feel more confident because i think she realized she was really shy, and she wanted to be more outgoing and meet people. and she wanted to explore dating. and that might not be how everyone else

thinks that dating should be. keith morrison (voiceover): what ashley is getting at is that mackenzie was active on dating sites, so much so that by saturday, june the 22nd, the sixth day after mackenzie's disappearance, detectives had received several phone calls from some of the men mackenzie met online, mainly to say they had nothing to do with her disappearance. i mean, nowadays, that's how people meet people. so while it was of significance because it gave us one more thing to look at, it wasn't this big huge red flag either. keith morrison (voiceover): so was mackenzie off on a lark with a guy she met online? a hookup she wanted to keep secret from her devoutly religious parents? well, that certainly seemed far more likely than some sort of kidnapping scenario. she could have gone camping or have gone with a friend where they would lose cell service, and it wouldn't be out of the ordinary.

keith morrison (voiceover): but once they did some checking around, that camping idea seemed a lot less likely. why? standard procedure-- they looked up airline flight records and discovered mackenzie had been booked on a flight out of town to las vegas. so maybe she was there. and meanwhile, the detectives began to see activity on her bank account and something else. different people stating, hey, i'm looking at her site right now. it's showing that she's actively online. keith morrison (voiceover): so maybe she was just fine, ignoring the fuss or zoned out and entirely unaware of it. and so we were hopeful. sure. because when people go missing, even if it's on their own accord, they're still going to be making transactions or paying for stuff. and so we're hopeful that there would be further transactions on there so that we could find her. keith morrison (voiceover): not far from the police station, kennedy and ashley hosted a rally to make sure everyone in salt lake city

knew to be looking for mackenzie. hey, guys, this girl is missing, and we're looking for her. she could be in danger. we think she's in danger. keith morrison (voiceover): but was she? on sunday, june 23rd, detectives learned, mackenzie had a flight booked for that very day, traveling from las vegas to los angeles to attend a friend's wedding. and she wouldn't miss that. so we contacted lapd, and they had officers waiting for that flight to land. keith morrison (voiceover): they waited by the jetway for all the passengers to deplane. mackenzie was not among them. then, they learned this. it wasn't mackenzie who had been logging into her social media accounts. that had been her friends. that have obtained her email and password. and they weren't doing it to try to ruin things or anything. they were trying to go on there to monitor the sites as well to see if any information could come up.

keith morrison (voiceover): and the activity on mackenzie's bank account? there was the lyft transaction on the 17th and then an automatic payroll deposit from her work. keith morrison (voiceover): and then the detectives got a tip from this guy, who just maybe could bring all those blurry details into sharp focus. andrea canning (voiceover): coming up. i got on the computer, and within an hour or two hours, i had found her profile. andrea canning (voiceover): the world of sugar babies. i think we're living in a culture where it's much more accepted and embraced for women to be upfront about what they need and want. andrea canning (voiceover): did mackenzie know what she was getting into? a lot of people who go into it are, like, seriously so blind to, like, the whole reality of what it is. andrea canning (voiceover): when "dateline" continues. when winter season hits emergen-c supports your immune system

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now. >> i'm jessica. >> layton with the hour's. >> top stories. former fox. >> news anchor and army combat veteran pete hegseth has been sworn in as secretary of defense after vice president jd vance cast the tie breaking vote to confirm him in the senate. >> it is only the second time. >> in u.s. history that a vp has done so for a cabinet nominee, and four israeli soldiers have been released in exchange for 200 palestinian prisoners. this is the second group to be released. by hamas into israeli territory. >> as part of a fragile. >> cease fire agreement. and now >> cease fire agreement. and now let's go back welcome back to "dateline." i'm andrea canning. where was mackenzie lueck? the college student took a lyft to meet someone in a park at 3:00 am. but who? mackenzie was active on dating sites, making police wonder if her late night rendezvous was a hookup, and her radio silence was intentional. now a tipster was about to share troubling details

of his encounter with mackenzie shortly before she went missing. here's keith morrison with "the waiting car." keith morrison (voiceover): it was a few weeks before mackenzie lueck vanished, a chance meeting at a bar with this man, rob joseph. she just seemed like a very bright, bubbly girl, friendly. keith morrison (voiceover): they talked for more than an hour, said rob, or she did while he listened. rob is an ex salt lake city cop, private eye now, which, of course, he told her. if you mention you're an ex-cop and you're a pi, everybody all of a sudden wants to tell you their dark secrets, you know, or risky behaviors. is that how people react, truly? oh, yeah, you'd be surprised that people just want to tell you things that you don't want to hear. keith morrison (voiceover): anyway, he only saw mackenzie that one time, he said. didn't get her phone number and--

and i didn't offer my number. i generally don't give out my number. keith morrison (voiceover): and that was that, he said. he didn't expect to see her again. but just three weeks later, mackenzie was missing. and rob said the friend who was with him at the bar that night made the connection. he just mentioned to me casually, hey, you know that girl we met at the bar, that's the girl that went missing. keith morrison (voiceover): of course, rob remembered the friendly college student and the secret she revealed to him that night. and i don't know whether she was seeking approval or just advice or recommendations and-- how did she put it? she said she was on a dating site and looking for sugar daddies, and i asked her which one. and she said seeking arrangements. keith morrison (voiceover): seeking arrangement, a website designed to connect young women with prosperous older men. rob knew a lot about dating sites. he's a pi, remember. and he figured if mackenzie was missing,

that just might have something to do with it. i went straight home, got on the computer, and got on to seeking arrangements. and within an hour or two hours, i had found her profile. keith morrison (voiceover): there she was, beachbaby96. what was interesting about her profile, it was just very authentic and honest. she wasn't really hiding who she was. she was pretty specific about, you know, she's a 23-year-old grad student at the u, studying kinesiology, california girl. you know, likes to drink wine, likes to go out, likes to travel, looking for somebody to do that with. a little more pg than some of them maybe? yeah. keith morrison (voiceover): soon as he found it, he sent a screengrab of mackenzie's profile to the salt lake city police department. this was definitely another avenue that we had to look at and track down anybody that might have been in contact with her. keith morrison (voiceover): mackenzie, it appeared, had compartmentalized information about her life.

the plane ticket to las vegas, for instance, had been paid for by a man she met through seeking arrangement. and a $300 deposit to one of mackenzie's bank accounts? that was from one of her other dates that she had been on that she'd received a payment from. and that was prior to her going over to her grandmother's funeral. keith morrison (voiceover): her friend ashley said she didn't have a clue. i didn't know anything about her being on that site, but-- she didn't talk about it. it wasn't like a subject conversation? not with me. keith morrison (voiceover): mackenzie's friend kennedy wanted to avoid the subject altogether, but she acknowledged that seeking arrangement is well known on campus. the site is not unfamiliar to a lot of women in college. everybody knows about it. everybody knows of this site. keith morrison (voiceover): seeking arrangement was founded in 2006 by a self-proclaimed nerd and mit grad named brandon wade.

he declined our interview request. but in this 2016 today show story, wade said he came up with the idea as a way to meet young women. the average sugar baby is roughly 27 years old. 50% of them are college students. they are ambitious. they are beautiful. and they are on the website because they want to find somebody who's successful, who's going to actually help them or spoil them. i think we're living in a culture where it's much more accepted and embraced for women to be upfront about what they need and want. keith morrison (voiceover): journalist mariella mosthof writes about sex and culture and sees sugaring as a form of female empowerment. and to hold power in a way that's open that is less stigmatized than it has been in the past. mm-hmm. so they would see this as holding power? i see it as very powerful, yes. explain that a little bit. any time you go into a relationship of any kind,

saying, this is what i need, and if you can't give me this, i'm going to move on, is a powerful thing to say. keith morrison (voiceover): there is some debate about this, whether it actually empowers young women or exploits the innocent. i mean, [sighs] a lot of people who go into it are, like, seriously so blind to, like, the whole reality of what it is, you know? keith morrison (voiceover): like mackenzie, tasia larkin from salt lake city had a seeking arrangement profile, but unlike mackenzie, tasia told us she was anything but a newbie when we spoke to her in 2019. at the time, the 20 something had been with a sugar daddy for six months. he was 63. do you mind telling me how much he pays you? my allowance is $1,200 a month. keith morrison (voiceover): tasia told us it took her a long time to find an arrangement. you have to fish through all of those guys who--

like, literally, they're like, let's meet up at a hotel, have sex, and i'll give you money. and i'm like, that's a prostitute. keith morrison (voiceover): shades of gray, can be confusing for anybody, said tasia, let alone a novice on seeking arrangement. i've seen girls who have had sugar daddies. they're not even the same person after it. did you read mackenzie's profile? yes, i did. she came from a very sheltered sort of upbringing. would that have made it more dangerous for her? oh, most definitely. going into it blindly is not something i would recommend. keith morrison: no. like, at all. welcome to let's talk sugar. this episode is all about getting ready for your sugar date. keith morrison (voiceover): seeking arrangement does make what they call let's talk sugar videos that offer up advice to novice sugar babies, giving tips on everything from how to ask for an allowance to what to pack in your purse.

perfume, they say, and pepper spray. not that you'll need it on your date, but going out looking hot is always a risk. keith morrison (voiceover): did mackenzie watch the videos? we don't know. but one of her decisions, said tasia, betrayed her lack of experience. why would you meet in the middle of the night in a park? keith morrison (voiceover): and there was something else. whether mackenzie did it or the person she met, we don't know. but remember, right after the lyft driver dropped her off at the park, someone turned off mackenzie's cell phone, which happens to be contrary to seeking arrangement's most important rule. you never want to get stuck homeless. that's your lifeline. mackenzie lost her lifeline, but before it went silent, she was busy texting. soon, investigators will follow her digital trail to the elusive man

who received those messages. andrea canning (voiceover): coming up. we've got an ip address that comes back to his residence. andrea canning (voiceover): tracking text messages. he said, well, i have an open wi-fi because i run an airbnb business. and so it could be anybody from here. did he run an airbnb business? andrea canning (voiceover): and a tip from a concerned neighbor. she described it as just being a really offensively smoky and very odorous. andrea canning (voiceover): when "dateline" continues. touch can mean so many things. even for people with moderate-to-severe eczema. touch can make two feel like one. or simply be a helping hand. dupixent can help you stay ahead of eczema as you welcome the feeling of touch. dupixent helps block a key source of inflammation inside the body that can cause eczema to help heal your skin from within. many adults saw 90% clearer skin. some even achieved long-lasting clearer skin

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keith morrison (voiceover): detectives in salt lake city were trying to find out if mackenzie lueck's disappearance was voluntary or not. remember the flight she was supposed to be on to los angeles? they found out it had been paid for by a sugar daddy. but remember, mackenzie wasn't on that flight. and they found out she wasn't on the one to vegas either. it was at that point that we were able to say, ok, we've got enough here that we can build our probable cause back up and really kick in and start serving some search warrants again. keith morrison (voiceover): and off the detectives went in search of the mystery person mackenzie was texting the night she vanished. with a 206 area code, conversation's going well before she left la to all the way to where she ended up in hatch park. keith morrison (voiceover): that digital trail eventually led them to a wi-fi router at this salt lake city house,

owned by a man named ayoola ajayi, aj, ex-national guard, successful tech worker, part-time model. police knocked on aj's door, talked with him, and found he was friendly, helpful. sure, he said, he had girlfriends, but mackenzie? they showed him a photo. and he-- told them he'd never seen that lady before. keith morrison (voiceover): so why, then, the police asked, did mackenzie get texts routed through aj's home wi-fi system? he said, well, i have an open wi-fi because i run an airbnb business. and so it could be anybody from here. did he run an airbnb business? he did. he rented out the two bedrooms down in his basement for airbnb. keith morrison (voiceover): they looked around, saw nothing amiss, and left. and then that same evening, aj stopped by the police station

to say he'd discovered something. it turned out he had texted with mackenzie lueck the night she disappeared. he'd forgotten, he said, because mackenzie was the one who reached out to him without identifying herself. maybe, he said, she'd seen his seeking arrangement profile. keith morrison (voiceover): said he had no idea who it was. keith morrison (voiceover): but she blew him off, he said, ghosted him. so he forgot all about her. but he told that story with so much confidence-- too much maybe? we had two different things now. we've got an ip address that comes back to his residence.

and now we know that he solely had contact with her. keith morrison (voiceover): except there was no proof mackenzie had been abducted by aj or anyone else for that matter. so he was free to leave. but before doing so, he gave the detectives his cell phone number, just in case they needed to get hold of him, a cell number actually registered in his name. remember, police didn't have that before. they just had that bogus 206 number used by the texting app. so now, with aj's personal cell number, they could get a search warrant for his call records and tracking data. and two days later-- we got the confirmation back from the fbi that mackenzie's records were showing her going from the airport to hatch park, and aj's records were showing going from his residence and also meeting up at hatch park at the exact same time. keith morrison (voiceover): and that was enough to get a warrant to search aj's home, where

investigators noticed a mattress was missing from the bedroom. and there was a strong smell of bleach. they also spoke with a concerned neighbor, her face blurred in this police video, who wanted the police to know that aj, the week before, had started an illegal backyard trash fire. and she described it as just being a really offensively smoky and very, very odorous. keith morrison (voiceover): debris even flew into the neighbor's yard. it looked like maybe they were clothing, pieces of, like, maybe fake leather or vinyl, something. we weren't sure what it was. what was it like for you when this discovery was made? i don't even know how to describe it. i mean, it was just a sinking feeling, really. i mean, we-- it's like we want to know what happened, but we also don't want to know what happened because if it's what we think happened, then we don't want to know that happened, if that makes sense. andrea canning (voiceover): coming up. that was probably the hardest part in the investigation is watching him walk out the door that night. andrea canning (voiceover): hard

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was already taken. get 20% off was already taken. get 20% off an welcome back. police finally discovered who mackenzie lueck was texting before she went missing-- a man who went by aj. he told detectives they never met in person,

but cell phone tracking data placed them at the same park at the same time mackenzie vanished. now investigators were closing in on their suspect. but were they getting any closer to answering a crucial question-- where was mackenzie? here's keith morrison with the conclusion of "the waiting car." keith morrison (voiceover): police looking for mackenzie lueck had heard a disturbing story from a neighbor who said ayoola ajayi had set a suspicious fire. the neighbor had found debris in her backyard. so they looked in aj's backyard and found something else disturbing-- a freshly dug patch of soil. they called in a cadaver dog, which gave the unmistakable signal-- human remains. aj, who had been calmly watching it all from his driveway, was taken into custody.

a team from the crime lab spent the night digging up the backyard. they found more burnt clothing, purses, or backpacks. and then down towards the bottom of the dig site, there was a very burnt and damaged iphone. and the medical examiner identified human tissue. keith morrison (voiceover): just fragments, mind you. they couldn't be certain who or even what they had exactly. we had these tissue samples or pieces. and so, in order to charge somebody or arrest them, that needed to be confirmed. and we knew that was going to take time. keith morrison (voiceover): so, without solid proof a murder had been committed, they once again, reluctantly, let aj go. that was probably the hardest part in the investigation, is watching him walk out the door that night. keith morrison (voiceover): mackenzie's friends heard he was released, and they

took it as a sign of hope. that maybe kenzie was still alive and he was hiding her because the police let him go the next day. keith morrison (voiceover): then at daybreak, detectives got a call from the state crime lab about the remains found in the backyard. they were able to identify that as being consistent with mackenzie. keith morrison (voiceover): the swat team took aj into custody, and police called a press conference to announce his arrest. we are filing charges of aggravated murder in the homicide of mackenzie lueck. keith morrison (voiceover): kennedy was watching on her cell phone. i almost blacked out or something. i dropped my purse, my phone. and i dropped to the ground on the street, and i was just bawling. i just couldn't even believe it. i still can't believe it. keith morrison (voiceover): but the detectives' work was not done. although they'd found human tissue in the fire pit

and linked it to mackenzie, they had not found her body. so the investigation continued. and once again, aj's personal cell phone gave him away. so that's my phone number. keith morrison (voiceover): remember, when he first spoke to police about mackenzie? well, the very next day, his cell phone pinged its way up into these mountains. about two hours north of here up to logan city, and then goes partially up to the canyon, and then returns back to salt lake city a couple hours later. so that was odd to us. keith morrison (voiceover): had he, a nervous killer, exhumed her body from that backyard fire pit to re-bury her up here? they set off to search logan canyon. and it took us a better part of the day until we found her. that's gotta be another tough part of your job. it was horrific. it was a sight that none of us wanted to see. keith morrison (voiceover): the search

for mackenzie was over. but the investigation was not. in the weeks following, a woman came forward to say she'd been sexually assaulted by aj a year earlier. at aj's residence, the same residence where mackenzie was killed. keith morrison (voiceover): she said she met him through a dating app, a religious one. aj was charged with aggravated kidnapping and forcible sexual abuse in that case. the evidence was tightening around him. evidence of what he did to mackenzie was growing. and finally, october 7, 2020, ayoola ajayi pleaded guilty to murdering mackenzie lueck. and as part of his plea deal, he admitted he thought about killing mackenzie, and then he planned the killing of mackenzie, a thoroughly premeditated murder. that he knew that he was going to murder mackenzie before--

before she even touched down at the airport. he kind of selected her as his victim. correct. was there any explanation at all of what his motivation was to do that? none. he never offered any reasoning of why or even how. keith morrison (voiceover): ajayi also pleaded guilty to sexually abusing his first victim. he was sentenced to life without parole. oh, and one more thing, said the detectives, he was active on the seeking arrangement site right up until he was arrested. even after we had made contact with him, he was still on that page, still trying to get a date. we don't know why some selfish jerk used his position on a dating website to somehow ensnare this bright, pretty woman. and for what?

i mean, you look at his profile pages on these sites, and he comes across as a gentleman, somebody that he truly isn't. and that's the whole cautionary tale, is you never know are they actually who they really say they are. keith morrison (voiceover): always, she'd been surrounded by people who loved her, worried about her, cared about her. mackenzie lueck was an innocent, setting out, if only for a moment, to explore new possibilities, unaware that in the world she was entering, the innocent can also be prey. that's all for this edition of "dateline." i'm andrea canning. thank you for watching. >> good morning, and welcome. >> to this sunday edi