>> a secret life uncovered. >> she was on a dating site looking for sugar daddies. >> going into it blindly is not something i would recommend. >> chilling details revealed. >> is this guy dodging us? >> he kind of selected her as his victim? >> correct. >> of course, the bottom of the big site there was a damaged iphone. >> it looks like maybe clothing. it was just a sinking feeling, really. >> i just ripley 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 were evil was hiding behind webs of lives. here's keith morrison with "the waiting car". >> 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 would want to imagine it? >> no, or anyone that i know. so, my mind didn't go there. >> 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. >> i saw that she was an opening my snap chats and i texted her. 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. >> 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 were all very close. >> 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. >> mackenzie's parents though, hadn't heard from her either. after three days of escalating fear, mackenzie's that made that most dreadful phone call to the salt lake city police department. >> yes, i'd like to get -- if possible, have a wellness check done on my daughter. i've been trying to get a hold of her and her phone just tends to go to voice mail. i was just wondering if i could have somebody maybe go by her house and check on her? >> the story mackenzie's that told was this. on the night of sunday, june 16th, 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 town house. her car was in the driveway. that was a good sign. repeated knocks at the door, however, went unanswered. peering through a window, the officers saw nothing. not a soul around. they 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 at the end of this unsettling day, mackenzie 's case was referred to a place that sounded very serious indeed. the salt lake city police departments homicide squad. >> we get a lot of missing persons cases in salt lake city. >> lieutenant todd mitchell was the units chief detective. >> so, i tried my best to sift through those and find the ones that raise that hair on the back of your neck, for the lack of the backer term. and this raise the hair on the back of my neck. so, that's why i decided, yes, we need to take action now. and at least are on an issue investigation into it. >> through three 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 sent silly text back and forth on a daily basis. >> detective and tiffany sayes levitate missing person investigation. even though their specialty was murder. >> we are, the usual homicide investigation, we start, there's a dead body. we were starting with something. we have a victim and we're moving backwards. in this case, we started with nothing. >> first action, sayes and wiley was to pull the salt lake city airport footage from the night of mackenzie's disappearance. and sure enough, there she was. >> so, there is nothing out of the ordinary. we are able to see her come off the terminal and we followed her all the way down to the baggage claim, where she picked up her luggage. >> seemed perfectly normal, fine, casual? >> yes. nothing out of the ordinary that we can seattle. >> 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 i heard about that, my stomach dropped. >> so, kennedy launched her own investigation. >> i went on facebook. i dropped pictures of us together and i said, she's missing. if you know anything, reach out to me. reach out, police. >> i thought she was still in california. until i saw kennedys message on facebook. >> ashley fine, another of mackenzie's college friends, put up her own facebook posts. >> and i tagged her in it and because i tagged her on facebook, some of her other family members reached out to me immediately. >> what family members? >> some of her distant cousins. 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 if, you're worried that maybe something happened in that car? >> definitely. definitely. >> on their own ashley and her cousin called lyft and uber, to see even 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. >> 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 north salt lake address and she was dropped off at hatch park in north salt lake, just before 3 am. >> a park? at 3 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? >> coming up -- mackenzie's friends have a terrifying theory about why she's missing. >> i assumed that the lyft driver abducted her. >> and here's one reason why. >> her last text message that we recovered was at 2:58, prior to her arrival arriving at the hatch park location. and that was the last activity ever we had on her phone. >> when "dateline" continues. s a cough, she takes robitussin. so, she can have those one on ones again. hey jim! can we talk about casual fridays? oh sure. what's up? get fast, powerful cough relief with robitussin, and find your voice. ♪robitussin♪ i have moderate to severe crohn's disease. now, there's skyrizi. ♪ things are looking up, i've got symptom relief. ♪ ♪ control of my crohn's means everything to me. ♪ ♪ control is everything to me. ♪ feel significant symptom relief at 4 weeks with skyrizi, including less abdominal pain and fewer bowel movements. skyrizi is the first il-23 inhibitor that can deliver remission and visibly improve damage of the intestinal lining. and the majority of people experienced long-lasting remission at one year. serious allergic reactions and an increased risk of infections or a lower ability to fight them may occur. tell your doctor if you have an infection or symptoms, had a vaccine or plan to. liver problems may occur in crohn's disease. ♪ now's the time to ask your gastroenterologist how you can take control of your crohn's with skyrizi. ♪ ♪ control is everything to me. ♪ ♪ learn how abbvie could help you save. teeth sensitivity is so common. it immediately feels like somebody's poking directly on the nerve. i recommend sensodyne. sensodyne toothpaste goes inside the tooth and calms the nerve down. and my patients say you know doc, it really works. my a1c was up here; now, it's down with rybelsus®. his a1c? 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[coughs] when caroline has a cough, she takes robitussin. so, she can have those one on ones again. hey jim! can we talk about casual fridays? oh sure. what's up? get fast, powerful cough relief with robitussin, and find your voice. ♪robitussin♪ for moderate to severe crohn's disease skyrizi is the first il-23 inhibitor that can deliver remission and visibly improve damage of the intestinal lining. serious allergic reactions and an increased risk of infections or a lower ability to fight them may occur. tell your doctor if you have an infection or symptoms, had a vaccine or plan to. liver problems may occur in crohn's disease. control of crohn's means everything to me. ask your gastroenterologist about skyrizi. ♪ control is everything to me ♪ learn how abbvie could help you save. ♪ control is keith morrison (voiceover): before mackenzie lueck >> before mckenzie disappeared disappeared in june 2019, a disturbing in june 2019. the disturbing story had gone national. several stories about women getting assaulted by using lyft or uber. >> 14 women have filed a lawsuit against the ride share giant. >> perhaps no surprise mackenzie's friend ashley fine imagined something like that or worse. >> i assumed the lyft driver abducted her or maybe they were in a car accident and had their car driven off the road. >> the detective thought that that was a possibility too, so they wanted very much to find that elusive lyft driver who gave her a ride the night she vanished. >> we wanted to know if he was in fact going to be a suspect or not. he was though, nowhere to be found. just as odd, mckenzie's phone, the detectives learned, was turned off just as her lift drive came to an end. >> her last text message that we recovered was at 2:58 prior to her arriving at the hatch park location. that was the last activity ever we had on her phone. >> on the morning of saturday june 22nd, six days after mckenzie went missing, detectives tracked down mckenzie'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? >> definitely. he did. he didn't seem like he had anything to do like this at all. >> 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 daytime and location all confirmed by the tracking software on his lyft apps. >> and he continue that throughout the night, and so -- >> you could eliminate him pretty easily based on the fact that he was elsewhere? >> very quickly, yes. >> she was smiling, she was in good spirits. >> mckenzie's lyft driver, told police and later us that he remembered the weird drop off location, even mckenzie commented on that, he said. >> saying how it was odd to be dropped off in the middle of the night in a park. >> he says that he wasn't worried because someone with a car was there waiting for mckenzie. >> i unloaded her luggage, said goodbye and drove away. >> so who was that someone in the waiting car? the detectives were hoping they could identify him or her through mckenzie's phone records. and she had been texting a number with a two zero six 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, it came back as nobody. >> and it had to be some type of burner phone. 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. >> but according to the lyft driver, whoever met mackenzie at the park, made no effort to conceal their identity from them. on the contrary. >> they seem to know each other. very well. i think all i heard was, how are you doing, how is your trip, basic greetings. the situation seemed very safe. she knew the person that she was getting in the car with. >> did mackenzie caught a car with someone that she knew, was both good and bad news? the good news, of course, was that it meant maybe mckenzie 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 search warrants. >> we had lost our, what we call, probable cause, that a crime had been committed. >> just like that? >> just like that. >> just because of what the lyft driver said, suddenly you can't be getting warrants for things? >> correct. that was a hard part and it's slow down the investigation at that point, because we didn't have a crime to attach to it, it was still now a missing persons investigation. >> without a warrant, the detectives were blocked from getting detailed phone records, which theoretically, would've shown who mckenzie was texting. so who was this friend mckenzie met at the park? where did they go? >> investigators are about to uncover fresh clues that deepen this mystery, but also give mckenzie's loved ones a glimmer of hope. coming up. one place mckenzie wasn't missing was on social media. >> different people saying, hey, i'm looking at her site right now and it is showing that she is actively online. >> her bank account was active too. >> so we're hopeful that there could be further transactions on there so that we could find her. >> when dateline continues. 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