this is "nightline". >> tonight. the chilling disappearance. >> i was panicked the minute she didn't come home on time. and i was doubly panicked when the dog was there and she wasn't. >> devastating her tight-knit community. >> everybody out there knows about mandy and what happened to her. >> now the stunning new interviews in the exhaustive search for evidence. and theunveiling an old crime, one woman helping to crack a cold case. >> he shot to the top of the suspect list.

>> night lynn will be right back.

"nightline" continues. here again, juju the story of mandy is the story of a young woman's

disappearance from a tight-knit, rural community. it's the story of a family devastated and a whole community devastated. it was a big deal. >> i was initially appointed sheriff in 2003. i went out and spoke with mandy's mother, mary, and told her that i was going to make every effort, that we would solve this case. >> i don't think i ever believed, ever, that they would catch the guy. >> the murder of mandy was a mystery. a decades-old cold case that left a small community on edge. >> it was so out of the realm of anything we could have ever expected. >> only solved by the combined determine's of loved ones, law enforcement, even strangers. the unexpected, avenevery day i that would crack everything wide open nearly 30 years later and

the shocking revelation of who committed the crime. >> couldn't possibly imagine it would be somebody we knew. >> the family lived out in acme, a little tiny town down highway 9 in rural watt kkin county. >> it's rural. not a lot out there, open roads, lots of cows. >> you knew your neighbor. you talked to your neighbor. >> everyone that lived out there, even today, knows about mandy stavik, and what happened to her. >> mandy had just graduated from high school. she was in her first year at central washington, at university. >> she came home for thanksgiving break. >> mandy left her home on the day after thanksgiving,98 he run. it was kind of in the late afternoon. >> she had a daily route that she used to jog that took her down the road that her house was

on, on strand road, down to the river and back. >> she went with their dog, kyra, a german shepherd dog. >> it was an older dog but very protective of mandy. >> i was panicked the minute she didn't get home on time. and i was doubly panicked a few minutes later and the dog was there and she wasn't. >> any kind of missing person call is a 911 call. it requires immediate response. and a deputy will go out and talk to the reporting party. >> in any investigation like this you're going to look at boyfriends, anybody they might have had trouble with. >> mandy's boy friend was cleared after he gave a police statement. >> in any investigation like this you'd have to figure out who mandy was, what she was about. >> she was very everything. i don't know whether there are words to describe her. >> mandy loved anything athletic. she could do things that i could never do.

she could jump on a horse bare back and take off running across the field. she loved softball, she loved track. she loved baseball. she loved basketball. >> everybody liked her, so she wasn't the typical student that, you know, may have one or two enemies. >> the search went on for three days. she was found on the third day. >> mandy was found on the south fork of the river, probably close to five and a half, six miles from her house. >> there was a bend in the river and some debris, and the body was just hung up in the debris there. >> i saw her body, she was face down. she was just kind of suspended, just a little bit off the bottom. there was a branch there that was some debris that prevented her from floating any further downstream. >> she was naked except for shoes and socks on. >> the tennis shoes match the description. >> the detective that was with me dispatched himself in a quick

fashion to get to the family home to let her know we had found her. >> i wouldn't wish this on even my worst enemy. there is nothing worse, there's nothing worse than losing a child. >> the medical examiner determined mandy's cause of death to be drowning. she'd suffered a head injury and had been sexually assaulted. >> they took dna evidence from mandy's body. they created a dna profile of both mandy and an unknown male. >> time and time again, they would have a person of interest. they would question that person. but something would rule them out. they had a good alibi, or ultirid match. this case dragged on. >> becomes a cold case. but after, you know, ten, 15, 20 years, you say ah, it's never going to be solved.

>> reporter: in 2013, a tip draws investigators' attention to mandy's former neighbor, tim bass. >> the case had never, never left the thoughts of mandy's friends. so two women were talking about the case and talking about what a strange person tim bass was. and they decided, we should talk to the sheriff's office. they should look at him. >> tim bass came up as a suspect. >> in 1989, tim bass lived on one side of highway 9 on strand road. and mandy lived on the other. >> he was a loner. he was a loner. he was quiet. may my impression was he was kind of an odd ball. >> he moved out of the area shortly after the murder. it was in january of 1990. he had quickly gotten married and moved to everson. >> i'm gina malone and tim bass

used to be my husband. he was very controlling and always told me what to do, what i could wear, what i couldn't wear. who i could talk to. who i couldn't talk to. whenever he'd get mad, he would, like, come towards me like this with his fist. he did shove me against the bathroom wall once. and bruised my back. >> 2010, gina had filed for a domestic violence protection order. that case was later closed, because she rescinded the domestic violence order, and they stayed married. >> reporter: when detectives visited gina and tim in their home they asked tim to give a dna sample. >> tim said he wasn't going to give us a dna, that he didn't trust the police, and it's kind of like, okay, what's plan b. >> 2017, since i didn't get a sample, we knew we'd have to do it surreptitiously. he was a route delivery person

for franz breads. >> we wasn't to franz and i met wagner for the first time. >> i met tim bass when he came to work with me. >> reporter: if detectives could acquire an every day item with his dna on it, they could run it through the lab to see if it matched the dna found on mandy's body. >> i said you want a water bottle? i can get you a water bottle. i need to know. >> we can't tell a person to get evidence for us. but if they were to bring something to us, we could take that from them and use that. that's not against the law. >> nobody asked me to do it, i 100% volunteered to do it. if something happened to my daughter, i'd want someone to help me, and the thought of her mom never having the answer of who did that to her daughter, if coy help her find that peace, i wanted to do it. >> she watched tim. they got a water cooler at their

office. and he drank out of a plastic cup and threw it away. >> he threw it in the garbage in front of me, walked past into the bathroom, and i looked in the garbage, and my heart was like, hmm, beating out of my chest. and i grabbed it, and i put it in my desk drawer. i think i waited a little bit, and i texted the detective. >> i couldn't get it back to the office quick enough and down to the lab quick enough to have it tested. >> reporter: but would tim bass be a match? and would mandy's mother find the justice she's seeking? stay with us. w sporty glc. come on. [ cars honking ] it's so late. yay. it fights traffic. no parking. -i told you. oh, a spot! hold on. it fights tension. seriously, did you take my phone? passenger light on. it even fights...fighting. innovation that keeps people together. the 2020 glc. lease the glc 300 suv

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>> it had been nearly 30 years since mandy stavik's body was found in a river. and police why were no closer to solving the murder. but law enforcement hopes that newly obtained dna pulled off a drinking cup used by former neighbor tim bass, will be what finally cracks this cold case wide open. >> when the cup arrived, i performed a swabbing of the drinking area. i pulled up the old information to compare it to, and let's just say i was more than surprised. it was a perfect match. >> when tim bass was taken into custody at his workplace, he agreed to talk to us down at the station. >> just like you've seen on t.v., on those shows you've watched, i just have to advise you of this before we talk to you any further, so -- you have the right to remain silent. >> tim's demeanor was flat. he didn't show a lot of emotion, tried to act like a lot of disbelief, like, "no, i didn't

have anything to do with this. you've got the wrong person. i've never had any intimate relationship with her. i've never even kissed her. >> he's testing the waters to see whether or not they actually have his dna versus them telling him a ruse. >> how'd that come about? my dna, that you guys got? >> i ran a sample. >> i don't remember giving dna. >> i'm sure in his mind, he was thinking, "i've gone through all these measures to make you guys didn't get my dna. how did this happen? where did i screw up? >> just tell me. if you just did it sneakily, you did something weird. >> well, of course i did. >> okay. well that's all you need to tell me. >> the point being is if i didn't have something of that nature, you wouldn't be sitting here. >> right. >> i think once he realized we actually did have his dna. then, he switched, "well, i wanted to tell you a long time ago but i just didn't trust you." >> i've been told not to say stuff.

ah, to hell with it. i can't do this. i can't. i trust you guys. i can't. if this bites me in the -- or this is not what i'm supposed to do, then whatever. i don't give a -- i slept with her. >> he completely does 180 degree turn. and at that point says, "yes, i slept with her." >> tim bass told us a story that he was having a secret relationship with mandy. >> and that's how he accounted for his dna being found. >> there's no way my sister would have had a relationship, a physical relationship with tim bass. she was way, way, way out of his league, to put it bluntly. >> you are under arrest for the murder of mandy stavik. >> the arrest occurred on december 12th, 2017. i filed charges, charged him

with murder in the first degree. >> shortly after mr. bass was arrested, i drove out to mary stavik's home. >> it was her 81st birthday that day. >> it was. it was on my birthday that he knocked on my door. kind of nice birthday present. >> she was overcome with emotion, and i think we all were. >> but the case wasn't closed yet. tim's wife gina tells police she spent that entire day with tim. >> when you went to his house that day, was tim there? >> yeah. >> he was there the entire time? >> yeah. >> despite the alibi, the case still went to trial, three decades after mandy had been found dead. >> to me, a trial is where i really love to be. >> all rise. >> finally getting underway was such a relief to me. the evidence will show that mandy was abducted, and we can tell you where it happened.

>> my theory is, is mandy set out to do her five mile run with the dog. about a quarter of a mile from her house where there's a wooded area, it's very secluded and that's where tim is waiting for her to run by. he grabs her, gets her in the car. >> she was taken approximately six miles south to an isolated location where she was raped. i think she tried to get away by running away, naked, wearing only her shoes and socks. >> he caught with her and hit her in the head and knocked her out. >> either struck in the head or pushed into a tree and then she was placed in the river where she was drowned. >> timothy bass's defense attorneys were trying to say that just because his dna matched that found in mandy's body, it doesn't necessarily mean that he killed her. >> did you ever see her with tim bass? >> no. >> one of the things i did with the witnesses i called, i asked each of them if they had ever seen mandy with tim bass.

no. never. >> we wouldn't hang out with him at all, ever. >> the main point was they didn't know each other, they didn't hang out together, they didn't run in the same circles. >> the state would next call gina malone. >> were you previously married to the defendant tim bass? >> yes. >> i filed for divorce. i only saw him one time in jail. >> by the time, gina bass walked into that courtroom, there's a lot of change in her life. gina came forward and said that her alibi that she originally told us was false. >> i believe gina was providing his alibi to protect herself and once she felt secure and safe herself, then she could actually tell the truth. >> after the police came, he told me that i need to lie and say that i was with him that day. and he said, "otherwise, i'm gonna go to prison." >> i felt like i just have to

agree with everything he's saying because if i don't, i could be next. i wasn't a strong person back then. i just was very weak. but i should've gone with my gut instinct. >> the day the verdict was read, the courtroom was packed. >> all rise. >> i understand that the jury has reached its verdict. >> we have. >> we the jury find the defendant timothy forrest bass guilty of the crime of murder in the first degree as charged in count one. >> tim bass was sentenced to nearly 27 years in prison. >> i thought, "hooray. the guy's going to get what's coming to him."

i give dave mceachran a lot of credit. he is something. and bless his heart, he told me day one that he was not going to give up until this was finalized. and we owe him the credit. >> up next, the moment mandy stavik's mom meets the woman who helped solve the case. ♪ we switched our detergent to one that's clean. ♪ ♪ and if you make the switch you'll see what we mean. ♪ ♪ tide purclean, because it's made with plants. ♪ ♪ tide purclean, gets stains out his pants. ♪ ♪ tide purclean, it has nothing to hide. ♪ ♪ it's made with plants and ♪ ♪ has the cleaning strength of tide. ♪ the first plant-based detergent with the cleaning power of tide. our because of smoking.ital. but we still had to have a cigarette. had to. but then, we were like.

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go safely, california. 30 daught daughter mandy was murdered, with the killer finally behind bars, she gets another moment of closure. >> i wanted to know so badly who did that and could meet you. id it for you. >> embracing the woman who helped solve her daughter's murder. >> thank you, thank you so much. thank you so much. >> you're welcome. >> person i wanted to meet for a long time is mary. all of it. i would do it again for her. a woman i never even knew.

>> mandy was special. she really was. i don't know why she was how she got to be the way she was. that's just the way she was. i kind of learned that the living have to go on to honor the goodness in what you've lost.

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