what she had was charisma. she said i love you and in my heart i knew those were her last words. >> two sisters with a single purpose, solved the mystery of their mother's death. >> we cannot let this go. >> she left for hawaii, a new life with a new husband but the sunny paradise soon grew dark. >> something is very wrong. >> it was horrible being so helpless. >> what was behind their moms death? they set out together to get some answers and they were about to get some help from their mother herself. >> a possible clue hidden in a envelope marked baby pictures, tucked inside a journal that painted a different picture entirely. >> i pulled out that envelope. >> reporter: could their mom help them solve their own mystery? >> we are her boys. we made a promise to our mom. >> hello and welcome to dateline. charlene was popular and unpredictable long before she had her girls kenny and tiffany. as children they adored their mother, as adults they made a troubling vow, promising charlene to investigate if she ever came to harm, then it happened charlene was dead and her daughters were suddenly detectives pursuing a mystery that would upend their lives. here is keith morrison with the bowel. >> here they were again. two sisters on a holiday in paradise or so the other vacationers must have assumed in the lush resort near honolulu but they would be wrong. this journey has more to do with a personal than any paradise. that and a long-ago promise to their mother. >> could you have believed you would be sitting in this hotel room talking about this subject in 2014? >> no. it is pretty crazy. i never saw this coming. >> perhaps it is crazy but there is apparently no stopping them. these tenacious sisters, tammy and tiffany. >> there is no halfway when it comes to a promise. it is all or nothing. >> bizarre story, yes it is. at the center of it is a woman named charlene. a beauty queen once back in colorado. >> my mother was a incredibly beautiful soul, she taught my sister and i that there was nothing we could not do. >> i love you. >> my earliest memories of her are her singing to me. she loved to sing and she played with me. >> my mother was a free spirit in many ways. she did not have a lot of rules, i do not have to do things like normal kids had to do but i liked it that way. >> so was often tammy and not her mother that took on the responsible role of little sister tiffany which was the other side of charlene's manic exuberance. >> she was unstable and she had a hard time taking care of herself much less anyone else. >> unstable. >> she would have highs and lows. >> moods, dark ones sometimes said the girls. >> she did not want to admit there was a issue. it was a hot button and it was not something you are ready to bring up unless you are ready for the fight. >> tammy refused to go with her. >> i said i cannot leave my dad. >> what did that feel like? >> like my heart was being ripped into. >> the girls lived apart for years until their father got custody of tiffany as well. then the girls watched and loved and worried about their mother from afar. then in the late 80s charlene found real happiness when she met and married a man named ken. >> she said i have never been with a man who really got me. she and her whole life never felt so utterly embraced by somebody that loved her the way she was. >> just because charlene dreamed of living in hawaii, can got a job here. >> she was a likable guy. he would always open the door for you. >> the sisters grew up and made lives of their own. tiffany moved to arizona, tammy settled in northern california and for a decade charlene seemed happy with ken. >> when did it change? >> it seemed to start to change around 1998. >> charlene told the girls that she and ken were fighting. in 99 she called upset and when they went to hawaii to see what was wrong she said the strangest thing. ask them to promise or something. >> she said promise me if anything happens to me you will investigate. we said what are you talking about? just promise me she said. >> surely left can soon after, moved to the mainland. the girls thought break was permanent and were relieved but seven months later. >> she said i am back in hawaii and i am back with ken and everything is fine. i do not want you to worry. >> worry they did. >> she would call me and talk about things. she would call me again a hour later and she would not remember anything we talked about. >> tammy sometimes did not pick up when her mother called but of course she had no idea what was about to happen. least of all in april 2000. >> my mom started calling my house and i was letting it go to voicemail and all of the messages were the same, she loved me. she found god. everything was fine. >> tammy waited until morning to call back. it was april 5. >> can answered the phone, he said i do not know what is wrong with your mother, you talk to her. i said hi mom, are you okay? she said i love you. her words were drawn out and slurred. i never heard that before. >> what was that like? >> i was in a panic. >> in a panic tammy called tiffany to tell her and then she called the honolulu police department. it was 6:00 in the morning there. she got a ambulance dispatched to the condo. >> my sister is the hero, she is sending an ambulance. >> the paramedics did not notice much to fix. the report states patient was conscious but under emotional distress, the spouse informed us she may have taken some aspirin with beer. the report continues, no empty containers of beer, no odor of alcohol on the patient, the patient said she was dying as well. very unusual but the emts did not take her to the hospital, left her home with ken instead. >> how is it possible? it was horrible. being so helpless. >> tiffany was so far away on the mainland in a panic trying to reach her mother calling repeatedly. ken finally answered. >> here i will put you on with her, you can talk to her. >> she said i love you and it was so hard for her to say it. the effort of moving her lips took so much. >> eight hours past and then at 2:00 can called 911. they rushed her to the er and did what they could. nothing worked. can called tammy from the hospital. tammy broke the news to tiffany. >> it went from just being in this place of utter desperation and helplessness and despair and uncertainty, and knowing in my heart she was gone. >> still barely hanging on on life support and that is when it began. with the first rush to their respective airports for flights to honolulu, no idea how long that journey would be or how hard that promise to keep. >> what happened to tammy and tiffany's mom? the sisters start their own investigation. coming up, a possible clue from their mother herself. >> she said if anything is to happen to me remember to ask for baby pictures. just remember that. >> when dateline continues. tel icy hot. ice works fast. ♪♪ heat makes it last. feel the power of contrast therapy. ♪♪ so you can rise from pain. icy hot. 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[ gasps ] [ chuckling ] good job, junior. way to go. [ chuckling ] [ speaking minionese ] sisters tiffany and tammy were transfixed, the contents of the envelope prepared by their mother for them and clearly marked baby pictures, but that was not what was in the envelope. instead they found notes written by ken. apparently a assignment for a anger management class. >> it was a journal on all of the different ways he abused her. >> i have spent on charlene, i have pushed charlene, i have yelled that charlene. >> suddenly the sisters believe their mother was sending secret clues that screamed open in case of death. they found a willing ally in the detective. one plan, secretly recording a phone call with ken. tammy made the call from that the police department. the strategy was for tammy to act friendly and supportive. ken told tammy he was deeply concerned for charlene. >> it is not the same without her here. i miss her very much. >> can also said he was suspicious of tammy and her sister. >> i get the feeling you guys are planning on ganging up on me or maybe sue me for manslaughter or murder or something. >> still he spoke with tammy at length about the day, charlene told him she took pills and seemed suicidal. >> she said she wanted to die? >> she said something like it is not working. for her to die. >> then after a pause he volunteered something that shocked them all. >> i guess i do not want to say it but she did say choke me so i can die. >> didn't you think to call the ambulance at that point? >> i thought she was being delusional, i was scared. >> he returned to the point he made before. >> i did not choke her. >> what a strange thing for him to say. >> he said a lot of strange things. >> now the girls believed they had to move fast while she was on life support. as long as she was alive they had the legal right to rummage through the garage of a house in california charlene kept looking for evidence against ken. so that is where they were when ken gave the order to take her off of life support. >> i was mortified and devastated again. >> at charlene's funeral according to the detective, ken's eulogy sounded like a well-prepared criminal defense. >> it started with charlene initiating sex the night before. that she was happy they were together. then he went on to how he tried to prevent her from dying. >> charlene's daughters were horrified, they were fully determined to keep their promise to their mother, they needed to ensure ken was charged with her murder. next to look at the case, prosecutor dan who found ken's remarks about strangulation very disturbing. here is why. >> this was viewed as a overdose, that is how the case went to the hospital and that is what any tiffany and tammy were thinking. >> yet as he began to dig deeper he found that can talked about strangulation more than once. >> he brought it up with the medical examiner's investigator. was basically telling them that this was not a strangulation case. >> in fact ken tried to persuade the examiner not to do a autopsy but of course there was one. the result took months but sure enough, cause of death, brain damage due to ligature strangulation. when a arrest warrant was issued the detective served personally. >> he said nick i did not kill my wife. >> in 2002, two years after their mother's death, tammy and tiffany came back to hawaii, this time to the courthouse for can went on trial for murder. >> he took the life of another human being and that human being was our mother. >> it was domestic violence at its ultimate. >> prosecutor dan quoted from dan'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 a investigator of the medical examiner's office. >> in court the medical examiner repeated her opinion that charlene was strangled, said she found ligature marks on her neck and the prosecutor played a tape of that recorded phone call with tammy in which ken brought up the idea himself. >> she did say choke me so i can die. >> i believe this was ken's subconscious talking. not a soul was thinking it was a strangulation case. until he brings it up. >> 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 rings. >> there is always a but, ken's defense attorney accuse police and prosecutors of jumping to the wrong conclusions, rushing to judgment against ken, the ligature mark must have been made by the two that was on her neck while she was on life support. this was not a strangulation he argued, not a murder at all as ken said all along. charlene took a overdose. >> because of her various mental disorders or defects, committed suicide. >> the trial lasted two weeks, the jury heard detectives, doctors and charlene's doctors of course. can chose not to take the stand. >> how was it going? >> it seemed to be going well. as if the promise would be kept but life as everybody knows is full of surprises. >> coming up, the verdict is swift but the real stunner was what came after. >> nobody stood up and said i object? >> it is amazing. >> when dateline continues. lin of moderate-to-severe asthma that's not for sudden breathing problems. dupixent can cause allergic reactions that can be severe. tell your doctor right away if you have rash, chest pain, worsening shortness of breath, tingling or numbness in your limbs. tell your doctor about new or worsening joint aches and pain or a parasitic infection. don't change or stop asthma medicines including steroids, without talking to your doctor. ask your specialist about dupixent. nexgard® plus helps you protect your dog from fleas, ticks, heartworm disease, and more... all in one delicious, monthly, soft chew. use with caution in dogs with a history of seizures or neurologic disorders. nexgard® plus: the one you want for one-and-done protection. 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