at the mountain source. our mother was an incredibly beautiful soul. what she had was charisma. she said i love you. in my heart i knew. those were her last words. >> two sisters with a single purpose -- solve the mystery of their mother's death. >> we can't let this go. it's heartbreaking. >> she'd left for hawaii, a new life, with a new husband. but the sunny paradise soon grew dark. >> something was very wrong it was horrible being so helpless. >> what was behind their mom's strange death? they set out together to discover the answer. and they were about to get some help from their mother herself.

>> there it was. evidence she left for you to find? >> yes! >> a possible clue. hidden, in an envelope marked "baby pictures." but tucked inside? a journal that painted a different picture, entirely. >> we pulled out the envelope and that was like, "wow." >> could their mom help them solve her own mystery? >> we can't quit. we are her voice. >> we made a promise. we made a promise to our mom. >> i'm lester holt. and this is "dateline." tonight, keith morrison with "the promise." >> reporter: here they were again. two sisters on a holiday in paradise. or so the other vacationers must have assumed here in america's mid-pacific garden. in the lush resort near honolulu. but they would be wrong. this journey has more to do with

a personal hell than any paradise. that and a long ago promise to their mother. >> could you have believed that you would be sitting here in this hotel room, talking about this subject, in the year 2014? >> no. it's pretty crazy. i could have never seen this coming. >> reporter: perhaps it is, pretty crazy. but there is apparently no stopping them, these tenacious sisters, tammy cocard and tiffany young. >> there is no halfway when it comes to -- to a promise. it's either all or nothing. >> reporter: bizarre story? oh yes, it is. at the center of it is a woman named shirlene van gundy. a beauty queen once, back in colorado. a girl who loved to dance and wear high heels. she was popular and unpredictable and kind of exciting. long before she became the effervescent mother of tammy and tiffany.

>> my mother was an incredibly beautiful beautiful soul. she taught both my sister and i that there was nothing that we -- we couldn't do. >> hi. i love you. >> my earliest memories of her are her singing to me. she loved to sing. and she played with me. she was -- she was a big kid. >> what was that like for you? >> oh, like i was the only child in the world. like i was her full focus and attention. >> my mother was a free spirit in many ways and didn't have a lot of rules. i didn't have to do things like normal kids had to do. like brush my teeth all the time. but i liked it that way. >> reporter: and so it was often tammie, and not her mother, who took on the responsible role with little sister tiffany, which was the other side of shirlene's manic exuberance. >> she was unstable.

and she had a hard time taking care of herself, much less anyone else. >> uh-huh. unstable. >> she would have the highs of highs and the lows of lows. >> reporter: moods. very dark ones sometimes, said the girls. >> she didn't want to really admit that there was an issue. it was a hot button, and it wasn't something that you wanted to bring up unless you were ready for the fight. >> reporter: when shirlene left the girls' father, tammie refused to go with her. >> i said, "i'm not going. i can't leave. i can't leave my dad." >> what did that feel like? >> like my heart was being ripped in two. >> reporter: the girls lived apart for years after that, until their father won custody of tiffany, too. and then the girls watched, loved, and worried about their mother mostly from afar.

and then, late '80s, shirlene finally found real happiness when she met and married a man named ken wakisaka. >> she goes, i've never been with a man who really got me. he gets me. she, in her whole life, i think had never felt so quite thoroughly and utterly embraced by someone who loved her just the way she was. >> reporter: and just because shirlene had dreamed of living in hawaii, ken got a job here and moved her to this condominium complex by a golf course on the pacific. >> he was a very likable guy. very -- very much a gentleman, always opened the door for you. >> reporter: the sisters grew up, made lives of their own. tiffany and her boyfriend, now husband, moved to arizona. tammie settled in northern california with a husband and two small children. and for a whole decade shirlene seemed so happy with ken. >> when did it change? >> it seemed to start to change around 1998. >> reporter: shirlene told the girls that she and ken were fighting. mid-1999, she called them, very upset, and when they went to

hawaii to see what was wrong, she said the strangest thing. asked them to promise her something. >> she said, promise me. if anything ever happens to me, you'll investigate." and we said, "mom, what are you talking about, if anything happens to you? "just promise me," she said. >> reporter: shirlene left ken soon after that. moved to the mainland. the girls thought the break was permanent. were relieved actually. but seven months later -- >> she said, i'm back in hawaii and i'm back living with ken and everything's fine. i don't want you to worry." >> reporter: but worry they did. >> she would call me and we would talk about things. and then she would call me again an hour later and she wouldn't remember anything that we talked about. >> reporter: it got so that tammie sometimes didn't pick up when her mother called. but of course she had no idea what was about to happen, least of all, one april night in 2000. >> mom had started calling my house, and i was letting it go to the voicemail.

and all the messages were pretty much the same, that she loved me, she found god, everything was fine. >> reporter: tammie waited until morning to call back. it was april 5. >> and ken answered the phone. and he said, "i don't know what's wrong with your mother. here, you talk to her." i said, "hi mom, it's tammie." i said "are you okay?" and she said. i love you. her words were very drawn out and slurred, like i'd never heard before. >> what was that like, that conversation, for you at your end? >> oh, i was in a panic. >> reporter: in a panic, tammie called tiffany to clue her in. still frantic, tammie then called the honolulu police department, it was 6am there. she got an ambulance dispatched to the condo. >> my sister is the hero. she's saving my mother's life right now. and it's the ambulance. like, they're gonna -- they're the professionals that are going to --

>> sure. they'll fix it. >> they're gonna fix it. >> reporter: but the paramedics didn't notice much to fix. their report states "patient was conscious but under emotional distress. she appeared calm but would not acknowledge our presence. her spouse informed us she may have taken some aleve aspirin with two beers." the report continues ...there were no empty containers of beer and no odor of alcohol on the patient. we were also informed by spouse that patient had said she was dying." very unusual indeed. but the emts did not take shirlene to the hospital. left her at home with ken, instead. >> how is it possible? how is it possible? this was horrible. it was horrible being so helpless. >> reporter: tiffany was so far away, on the mainland, in a panic, trying to reach her mother. calling repeatedly. ken finally answered the phone. >> "here, i'll put you on with her. you can talk to her." and she said, "i love you."

and -- and it was so hard for her to say it because the mere effort of moving her lips took so much. >> reporter: eight long hours passed, and then, at 2 pm, ken called 911. they rushed her to the emergency room, did what they could. nothing worked. ken called tammie from the hospital. tammie broke the news to tiffany. >> it went from, you know, just being in this place of such utter desperation and helplessness and despair and -- and uncertainty, like, and knowing in my heart that she was -- she was gone. >> reporter: though still barely hanging on, on life support. and that's when it began with that first rush to their respective airports for flights to honolulu. no idea how long that journey would be. how hard that promise to keep. >> what had happened to their mom? when we come back, the sisters

start their own investigation. >> most people would just leave it to a police department to do the investigating. not you two? >> no. >> and they'd find a possible clue from their mother herself. >> she said, "if anything ever is to happen to me, i want you to ask for your baby pictures. remember that, okay? just remember that.

>> reporter: six anxiety-filled hours. on the long plane ride to hawaii, all sisters tammie and tiffany knew was that their mom was on life support. they weren't sure why or even what exactly happened to her but during those six hours they had plenty of time to reflect on what she said to them nine months earlier. >> promise me you'll investigate. if anything happens to me, you'll find out what happened. >> reporter: they'd promised, of course.

though even before they even got on the plane for hawaii, they called the police to report that they already had their suspicions. and those suspicions were all about shirlene's husband, ken wakisaka. >> i heard from tiffany before i even went to st. francis west. i was assigned the case by my lieutenant, and he said, "before you go, call this girl." >> reporter: tiffany told detective nick cambra about her pre-flight conversation with the hospital. >> i asked the emergency room attendant -- i'll never forget this. i said, "where's ken?" and he said, "he went home to feed the dogs." i said, "so she's there by herself? well, who does that? >> reporter: by the time detective cambra got to the hospital he had been told what tammie and tiffany had suspect, that shirlene had taken or been

given an overdose of pills. he also heard from medical personnel they thought ken's behavior seemed strange. though no one, including the ambulance driver, could quite say why. >> he also related that the husband was acting suspicious. >> reporter: did he say how? >> he said he -- just the way he spoke and the way he acted. >> reporter: suspicious? >> yes. >> reporter: when detective cambra heard that ken left the hospital while his wife was lying in a coma in the icu, he wondered, was ken going home to cover up a crime scene? and when cambra checked to see if ken had a record of any kind, he discovered, yes, he did. >> i did pull police reports of ken. ken had been arrested for abuse. >> reporter: it gave cambra pause and made him consider what he'd already heard from tiffany. >> that her mom had said she would never commit suicide and that she was afraid that ken was trying to kill her prior to this incident. >> reporter: now, in hawaii, at

their mother's bed in the icu, tammie and tiffany vowed to find out what exactly happened to their mother. you know, most people would just leave it to a police department to do the investigating. not you two? >> no. >> reporter: first target? ken and shirlene's condo. must be evidence there, they decided. so they made up a story for ken, told him they needed a rest after their long flight. could they borrow a bed in the condo? and, sure enough, he gave them the keys, while he stayed at shirlene's bedside in the hospital. >> when he was there, what did you guys do? >> we went to the house. >> in ko olina. >> reporter: to do what? >> to see what we could find. >> reporter: just kind of look in cupboards, and under beds and in closets for what kind of stuff? >> for things that we thought that might help us to figure out what happened that day. >> reporter: because shirlene sounded so out of it on the

phone, and ken mentioned pills to the emts, tammie wondered if her mother took pills. in fact, the hospital was treating it as an overdose. but the sisters did not believe she did it deliberately, so they went looking for those pill bottles. >> and we had looked through the house and couldn't find them. and so we were out in the backyard, just looking. and sure enough -- >> reporter: in the backyard? >> underneath a bush. >> reporter: as if they'd been hidden there or what? >> yes. >> reporter: in their minds, only one person could have hidden them, ken. later, as tiffany and tammie were about to drive away from the condo, having thrown in the back seat a sealed envelope ken had left out for them. suddenly tiffany remembered something else her mom told her. >> she says, "tiff, i have to tell you something, and it's important." and she said, "if anything ever is to happen to me, i want you to ask ken for your baby pictures. remember that, okay? remember

that." >> reporter: and, sure enough, that appeared to be what ken had just given them. they tore open the envelope and inside? most definitely not baby pictures. >> coming up -- there it was, evidence she left for you to find? >> yes. >> what could be a revealing clue from their mom, and a revealing chat with ken. >> what did he say in that telephone conversation? >> when "dateline" continues. who are these people? the energy conscious people among us say small actions can add up to something... humongous. a little thing here. a little thing there. starts to feel like a badge maybe millions can wear.

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>> reporter: sisters tiffany and tammie read, transfixed, the contents of an envelope prepared by their mother, for them, and clearly marked "baby pictures." but that is not what was in the envelope. instead they found notes, written by ken, apparently an assignment for an anger management class. >> it was actually a journal about all the different ways that he'd abused her. "i have spit at shirlene. i have yelled at shirlene. i have pushed shirlene." >> reporter: there it was in his own hand, evidence she left for you to find? >> yes. >> reporter: and suddenly the sisters truly believed their mom was sending secret clues that almost screamed "open in case of death." attempting to solve the mystery, they found a willing ally in detective cambra. one plan they came up with together? secretly recording a phone call with ken. tammie made the call from the police department.

the strategy was for tammie to act friendly, supportive. >> hello. >> ken? >> yeah. >> hey, it's tammie. >> reporter: ken told tammie he was deeply concerned for shirlene. >> i love her. it's not the same without her here. i miss her very much. >> reporter: but ken also said he was suspicious of tammie and her sister. >> the feeling i'm getting is like -- i'm feeling like you're going to plan on ganging up on me. and it sounds like you're going to maybe sue me for manslaughter or something, or murder. >> reporter: still, he spoke with tammie at length about the day. he said shirlene told him she took pills and seemed suicidal. >> she said she wanted to die? >> yeah. she did say something like, "it's not working. it's not working." >> it's not working? >> yeah, like for her to die. she's saying, "it's not working." >> reporter: and then, after a pause, he volunteered something that shocked them all. >> i guess -- i don't want to say it. but she did say, "choke me so i could die."

>> she said that? >> yeah. she said please choke me. >> oh, ken, didn't you think at that point you should call the ambulance? >> no, because i thought she was just being disillusional. i was really scared. >> reporter: but he then returned to the strange point he made before. >> i haven't choked her. there's no, you know, choking marks around her neck. >> right. >> you can have the doctors check that out. >> reporter: what a strange thing for him to say. >> he said a lot of strange things. >> reporter: now, the girls felt they had to move very fast, while shirlene was on life support. as long as she was alive, they decided, they had the legal right to rummage through a garage in a house in california shirlene had kept looking for evidence to use against ken. so they flew to the mainland. and that's where they were when ken gave consent to take shirlene off life support and she died. >> and i remember thinking -- and just bawling my head off again. so i was mortified. and i was devastated again that

i wasn't there. >> reporter: at shirlene's funeral, according to detective nick cambra, ken's eulogy sounded like a well-prepared criminal defense. >> he started with that shirlene initiated sex the night before, that she was happy that they were together. and then he started -- he went on to the next day and how he tried to prevent her from dying. >> reporter: shirlene's daughters were horrified. now, they were fully determined to keep their promise to their mother, they'd need to ensure that ken was charged with her murder. next to look at the case, prosecutor dan oyasato, who found ken's remarks about strangulation very disturbing. and here's why. >> this was viewed as an overdose. that's how this case went to the hospital. that's what tiffany and tammie were thinking. that's what the police department was thinking. >> reporter: and yet, as oyasato began to dig deeper, he found that ken talked about

strangulation more than once. >> he brought it up with the medical examiner's investigator and was basically telling them, "this is not a strangulation case." >> reporter: in fact, said the prosecutor, ken tried to persuade the examiner not to do an autopsy. but, of course, there was one. the result took months but, sure enough, cause of death, said the medical examiner, brain damage due to ligature strangulation. when an arrest warrant was issued, detective cambra served it personally. >> police arrested 45-year-old kenneth wakisaka tonight. prosecutors say he strangled his 52-year-old wife last april. tonight, police charged him with murder in the second degree. >> reporter: how'd he react? >> he said, "nick, you know i didn't kill my wife. i didn't kill my wife." >> reporter: in 2002, two years after their mother's death, tammie and tiffany came back to

hawaii. this time to the courthouse where ken wakisaka went on trial for murder. >> he took the life of another human being, and that human being was our mother. >> this was a murder by strangulation. it was domestic violence at its ultimate. >> reporter: in his opening statement, prosecutor dan oyasato quoted from ken's own statements to accuse him of murder. >> can you tell if a person has been strangled during autopsy? these are the words of the defendant to an investigator from the medical examiner's office. >> reporter: in court the medical examiner repeated her opinion that shirlene was strangled, said she found ligature marks on her neck. and in court the prosecutor played a tape of that recorded phone call with tammie, in which, sure enough, ken brought up the idea himself. >> i guess -- i don't want to say it. but she did say, "choke me so i could die." >> i really believe this was ken's subconscious talking out.

no one, not a soul, was thinking this was a strangulation case. >> reporter: until he opened his mouth and -- >> until he brings this up. >> reporter: that made everybody suspicious. >> every witness who testified as to having some contact with ken spoke about his unusual behavior. his focus was not on his wife. it was on other things. >> reporter: but! there's always a but. ken's defense attorney, mal gillin, accused police and prosecutors of jumping to the wrong conclusions and rushing to judgment against ken. that ligature mark? must have been made by the tube that lay on her neck while she was on life support. this wasn't a strangulation, he argued, wasn't a murder at all. as ken had said all along, shirlene took an overdose. >> mrs. wakisaka, because of her various mental disorders or defects, committed suicide. >> reporter: the trial lasted

two weeks. the jury heard detectives, doctors, shirlene's daughters, of course. ken himself chose not to take the stand. how'd it seem to be going? >> it seemed to be going well. >> reporter: as if, here, their promise would be kept. but life, as everybody knows, is full of surprises. >> coming up -- the verdict would be swift, but the real stunner was what came after. >> nobody stood up and said, "i object, your honor." >> it's amazing. it haunts me. i'll tell you right now, it haunts me. the home of "wow" savings.

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>> reporter: two tenacious daughters made a promise to their mother and were hoping to keep it. but now, it was up 12 other people, a jury. were you in the court when the verdict was read? >> yes. >> reporter: tell me about that. >> what a huge relief to hear those words, "we, the jury, find ken wakisaka guilty of murder in the second degree." it was amazing. ken was -- well, surprised would be an understatement. >> i didn't expect this at all. >> reporter: but these two? >> i was a really happy girl.

you know, i'm like -- the system worked. you know, it worked. >> reporter: ken, who still maintained his innocence, was sentenced to life in prison. and that would be it, end of story. except -- coincidence is such a strange and powerful thing, isn't it? it's a curious story the way you encountered this case, hmm? >> yes. i was visiting another client who had been charged with murder. >> reporter: defense attorney john edmunds doesn't normally find new cases in prison, but something seemed very credible about this particular client referral. >> he turned to me and he said, you know, "my cell mate, who's out in the rec yard right now, doesn't belong here. there's something really odd about his case. would you look at it and see what you think?" >> reporter: so edmunds agreed to at least have a look at the record. a thick file of transcripts, hundreds of pages. and late one night, he was sitting up in bed beside his wife, reading every word said at ken's trial.

and suddenly, there it was. eureka. >> and i get to the final argument. and the prosecutor makes a direct comment upon mr. wakisaka's failure to take the witness stand. >> reporter: this is what edmunds read. it's in prosecutor dan oyasato's final argument, his own words, "who was alone with her? he was alone with her. he was there. he would know. if he doesn't tell us, we can only look to shirlene and see what her body tells us." >> the fifth amendment privilege against self-incrimination is a constitutional right that can be rendered meaningless if the prosecution gets to comment on it. >> reporter: and nobody stood up and said, "i object, your honor?" >> it's amazing. the trial lawyer said nothing. the judge said nothing. >> reporter: those five words, "if he doesn't tell us," would be the basis for edmund's appeal. >> the most serious offense is commenting on the failure to take the witness stand. but we're supposed to be

professionals, and we're not supposed to make those kinds of mistakes. >> reporter: did you write your closing argument? >> i write an outline. i commit it to memory. >> reporter: so, how did that line come out? prosecutor oyasato said it was a mere slip of the tongue. >> what i was trying to do with that statement was actually transition from, if he doesn't know, then we need to look at her body. we need to look at the rest of the evidence to tell us the story. >> reporter: none of this seemed like such a big deal to shirlene's daughters. >> people file appeals all the time. i understood that. but i wasn't paying attention anymore because it was done. >> reporter: oh, but it wasn't done. in 2003, a year after the trial and three years since shirlene's death, hawaii's supreme court handed down its decision. >> i got the call from dan oyasato, the prosecutor. and he said, "the verdict's been overturned." >> reporter: overturned. the guilty verdict the daughters so desperately wanted, pulled out from under them just like that. >> he goes, "it wasn't the evidence of the case.

it was on the 5th amendment. it was prosecutorial misconduct. that's my fault." >> reporter: so he took responsibility for it right away? >> instantly, instantly. the pain that he felt, because he worked so hard. >> it haunts me. i'll tell you right now, it haunts me, you know, that i did this. i have apologized i don't know how many times to the girls because of my error. >> reporter: still, said the sisters, the ruling didn't mean ken was innocent. far from it. >> even though the verdict was overturned, it was overturned on technicalities and not on any evidentiary issues. >> reporter: and they found a small silver lining. the supreme court said ken could be re-tried. >> and so that left the door open for us to bring it back to trial. and we just needed to try again. >> reporter: so they took it upon themselves to pick up right where they left off. after all, a promise is a promise.

>> i just remember thinking, "okay, so we need to keep pushing." >> you can't quit because there is no other option. because you can make a difference. >> reporter: ken got out on bail, but was still under indictment for murder, and they all waited for the new trial. and then, once again, john edmunds put on his reading glasses. >> and what i found again stunned me. >> coming up -- >> i went over to talk to the emt. >> a possible new witness with a very different story to tell. >> i couldn't believe it. i still don't believe it. >> when "dateline" continues. - "once upon a time a little girl

learned how to read."

her mighty parents kept the adventure going by reading her books that were beyond her skill level. her mind and her imagination grew happily ever after. >> reporter: ken wakisaka, convicted of killing his wife shirlene, was out on bail, guilty verdict overturned thanks to an error discovered by ken's new defense attorney, john edmunds. but edmunds wasn't finished digging, and pretty soon he found another error, a big one, that occurred even before the trial. >> there was a witness that the grand jury asked to be called, whom the prosecution didn't call. >> reporter: thing is, it's an iron-clad rule. if a grand jury asks to hear from a witness, the prosecution must comply. didn't in this case.

it wasn't a minor witness, either, said edmunds, but someone in a position to know a great deal about what really happened to shirlene. >> the wakisakas had an upstairs room that they rented out to a guy, and he had been there and seen a lot of what went on that morning. >> reporter: though the grand jury didn't hear from the roommate, detective nick cambra did. cambra asked him, what did shirlene say to ken on the day she died? the defense provided us an excerpt of detective cambra's interview with the witness. >> she was asking ken to come here, you know, be by my side. she did say she wanted to die in peace. >> reporter: testimony that seemed very much in ken's favor, testimony the grand jury that indicted him never heard. defense attorney edmunds again went to court, and again won. so tell me, from a practical point of view, what did those victories mean for ken? >> well, from a practical point of view, it meant that indictment got dismissed.

>> reporter: dismissed. as if he'd never been charged in the first place. ken was no longer free on bail. he was simply free. >> and now we're back to a point as though the case never was brought in the first place. and that's frustrating. >> how do you get your head around it? how do you process all of it? how do you move forward every day? >> reporter: and how would they make the case against ken and persuade the state to start from scratch? ken's story had never changed, that shirlene killed herself, accidentally or on purpose, with an overdose of pills. of course, the state still had evidence, like that pill bottle the sisters said they found stashed in the back yard of the condo, as if ken fed the pills to shirlene, then tried to hide the bottle from the police. but defense attorney edmunds could show ken didn't try to hide anything, that, in fact, he took paramedics to the medicine cabinet himself. >> they counted down tablets in a bottle of pills to see how many were left, and how many -- tried to figure out how many

she'd taken. which is what she said she had done. >> reporter: and there was a potential new defense witness who knew shirlene well, didn't like her at all, in fact. and she has her own strange theory on what happened to shirlene. >> you get to know the people who are living in your -- >> you have to. >> reporter: -- building, yeah. marjorie collier managed the condominium complex where shirlene and ken lived. unlike the daughters, marjorie considered shirlene the dominant, even abusive, force in the marriage. >> she used to tell me that ken was the complete opposite of her, that he was very quiet, and he would never argue with her or get into a fight with her. he'd leave the building. >> reporter: yeah. >> he'd just go for a walk. >> reporter: how'd she feel about that? >> she didn't like it. >> reporter: marjorie was on the scene april 5th, 2000, after tammie called 911, urging emt's to check on her mother. >> i went over to talk to the emt. and he said, "well, she's awake, and she's coherent enough to tell us that she's not coming with us."

and i said, "oh, okay." >> reporter: remember, in the official emt report, it was ken who said shirlene didn't need to go to the hospital. but marjorie insisted an emt told her it was shirlene who refused to go. so, your memory of that's pretty clear? >> i'm positive. >> reporter: when you heard that ken was accused of strangling her -- >> i was absolutely shocked. i couldn't believe it. i still don't believe it. >> reporter: but, what does she believe about how shirlene died? well, just her speculation, of course. it's based on an incident that began, she said, when shirlene was making a fuss in the condo office. >> and she was being very pushy. and i went to shut the door, just to get her to go home, because i wasn't even open yet, and the door hit her arm. and she spilled her cup of coffee. >> reporter: the next thing marjorie knew a police officer was threatening to arrest her. >> and i said, "for what?" and he says, "for abuse."

i said, "excuse me." and i looked at shirlene. and from her thigh, mid-thigh, all the way down to her feet, was burned, severely. >> reporter: you're kidding. >> burned, more burned than you get laying out in the sun all day. >> reporter: was it from that coffee? >> that's what she said it was. but the police officer told me one cup of coffee won't burn both those legs like that. >> reporter: both legs were burned? >> yeah, she burned her own legs. in that case, marjorie believed, shirlene was willing to hurt herself just to frame marjorie. so, when shirlene died? >> what i thought, honestly, was that it was another ploy, and she had tried to make it look as if he was trying to kill her, and she went too far and accidentally killed herself. >> i think that that's marjorie's perspective. do i think that she's correct in her opinions? no, absolutely not.

>> reporter: to shirlene's daughters, there was still no doubt about what really happened and what to do about it. i think your mother had a word, didn't she, that she liked. what was that word? >> tenacity. >> i just had to keep going. and here's the thing about keeping going, by doing something, in the process, i was honoring her. >> reporter: tiffany filled a suitcase with documents that some prosecutor might find useful, hauled it back and forth to prosecution meetings, pushing for action for years. >> well, i kept going to hawaii for sure. i'm, like, "pardon, hi. it's me again. my mom -- what's going on with my mom's case?" >> reporter: by this time, dan oyasato no longer worked at the honolulu county prosecutor's office. and the prosecutor who took over the case seemed reluctant to go forward. but that wasn't going to stop shirlene's daughters, not for one minute. >> we had a guilty verdict.

we need to move forward. we need to re-charge. we need to re-indict. we need to go back to trial. >> reporter: but, it turned out, a big surprise was coming, this time from the prosecution. >> coming up -- a whole new theory of the case. a change for prosecutors. a challenge for that promise. >> how long are you prepared to do this? >> as long as it takes. we made a promise. celebrate the summer of heroes, only at disneyland resort. hero up!

>> reporter: april 2014, tiffany and tammie returned to hawaii where they marked a painful anniversary, 14 years since their mother, shirlene, died. >> it's heartbreaking.

>> reporter: why do you say heartbreaking? >> we've spent all these years trying to get justice. >> we made the promise to my mother that we would investigate, therefore it has to be, therefore you can't quit. >> reporter: the daughters thought they'd made good on their promise to find justice for their mother if anything happened to her when shirlene's husband was convicted in 2002 of murder by strangulation. but that verdict was overturned in 2003. then, ken's original indictment was thrown out two years later. you thought maybe a few months it'd be back in court? >> not a few months. i thought within a few years. >> reporter: but the years just kept passing. ken has moved on, though he still lives in the same condo. >> he is happily married. he is employed, works for a construction company as a quality control manager. >> reporter: but tammie and tiffany say they can't move on, and they acknowledge it's been hard on their husbands and children. >> i feel really bad for my family because it's not their

mother. they didn't make the promise i did. because every time i'm not there someone else has to cover all the things that i normally do. >> reporter: tiffany, especially, makes the trip to hawaii repeatedly, and kids and husband know they're on their own whenever she rolls out the suitcase stuffed with case papers. >> yeah, that's the signal. there simply is no other room in those moments for much of anything else. >> reporter: still, they push on. >> we will get a conviction. and i will do everything i can possibly do in order to make that happen. >> reporter: the case has dogged detective, nick cambra, too. he's retired now, but he counts the years and wonders. do you perceive enthusiasm in the prosecutor's office to -- >> not at all. >> reporter: -- to go after this? >> not at all. >> reporter: they would do so reluctantly? >> yes. >> reporter: but why? if prosecutors won a conviction once, why not just do it again? >> at this point it's not my decision. but what i can say is, provided the evidence was not suppressed

and is still available, there is more than ample evidence to prove his guilt. >> reporter: anticipating a new trial, defense attorney edmunds hired renowned forensic pathologist, michael baden. >> and asked him, "what is your opinion? was there strangulation or not?" he said absolutely not. he said, "this is just wrong." >> reporter: so the new prosecution hired its own experts, and, well, it didn't go as planned. >> the new prosecutor on the case said that they had one or two forensic pathologists who agreed with dr. baden. >> reporter: they agreed that shirlene wasn't strangled. but these are prosecution experts. did that surprise you? >> it did. >> reporter: yeah. >> i don't think that they provided all the information that the expert needed in order to make that determination. >> reporter: the prosecution announced in court in 2010 it was abandoning the strangulation theory, the very theory that got ken convicted in the first place. what did you think when they just dropped that theory?

>> i was shocked. honestly, i was shocked. >> reporter: the current prosecutor declined to talk with us, or share any information about the case. but in an e-mail to the daughters, from january of 2014, he said his boss, the chief prosecuting attorney referred to here by his initials "kmk," "gave the green light to go forward." go forward with what? a whole new theory called murder by omission. what's your understanding of what murder by omission is? >> my understanding is that it's a duty of a spouse or a parent to get medical help for someone who can't get help for themselves. and if they die because of that, then you've effectively committed murder. >> reporter: in the e-mail, the prosecutor told the girls, he just needed one or more experts to give the opinion that "wakisaka's failure to perform his duty to provide timely

medical care for shirlene caused her death." despite abandoning the strangulation theory, the prosecutor, in his e-mail, now said he might actually bring it back, along with murder by omission, for a possible new trial. do you really think they will? >> have they? >> reporter: have they? >> no, they have not. they've done nothing. >> reporter: so, what stage are you at? believe it when you see it? >> absolutely. prove me wrong. show me that you're going to do something. quit leading us on to believe that you're going to move forward with a case that we've been hanging onto for ten years. >> reporter: defense attorney edmunds said he would knock down the prosecution's new omission theory by pointing out that ken did try to get help for shirlene by calling 911. so far, there has been no move to charge ken, and it's not clear when, or if, there will be.

>> i don't think you could fault these two women for how they feel about the loss of their mother. >> reporter: they had been tenacious. >> tenacious. >> reporter: you'd agree with that? >> yes. doesn't mean they're right. >> reporter: ken has maintained his innocence all these years, even though shirlene's daughter's quest to prove him guilty goes on. >> he's very troubled by it. >> reporter: is he living under a cloud now? >> he feels he is. he'll never really be at peace. now, more people recognize him on the street. that's embarrassing. >> i miss her so much, tammie. >> me, too. >> reporter: call it a promise, a quest, an obsession. her daughters' journey isn't over. how long are you prepared to keep going with this? >> as long as it takes. >> reporter: i mean, you could

be sitting here an old lady and, years and years from now, and nothing will have happened. >> we made a promise. we made a promise to our mom. >> it is with such purpose and such passion and such love that i do this. it is in honor of my mother. i don't care if it's labeled obsession or crazy. i'm doing this because i love her. and she deserves it. >> reporter: that's all for now, i'm lester holt. thanks for joining us. next at 11:00, two boys killed in a violent hit and run crash. we learn about the driver in police custody. president trump makes new comments about two msnbc anchors, next.

right now at 11:00, two young boys killed in a hit and run crash in concord. what we know about a person detained by police. >> the news at 11:00 starts now. good evening and thank you for joining us tonight. >> a family torn apart after a tragic crash in a dangerous 24 hours on bay area roads. the person of interest in a deadly hit r