>> that's all for this edition of "dateline." i'm craig melvin. thank you for watching. i'm craig melvin. >> i'm natalie morales. >> and this is "dateline." i know my sister would have fought. we used to tell each other that if somebody ever tried to hurt us, that we would do everything we can to leave something behind so the other one can figure it out. i believe that she was murdered. >> this is a very bizarre death. >> it was baffling from the start. a young woman dead at her millionaire boyfriend's mansion. >> 911 emergency, what are you reporting? >> yeah, i got a girl, hung herself. >> my heart started racing. >> reporter: you found her hanging? >> i did. >> detectives ruled it a suicide. but was it? at the scene -- knives.

ropes. a cryptic phrase. >> her hands were tied. her feet were tied. she was naked. >> this was sending a message. >> that wasn't the only suspicious death here. >> no mom wants to hear that her son was the victim of a homicide. >> something happened at the top of the stairs. >> what really went on in that mansion? hear from the man at the center, in his first television interview. >> reporter: you thought you had nothing to hide. >> i knew i had nothing to hide. >> the worst shock in probably my entire life. >> hello, welcome to "dateline." victims' families have often described their feeling of loss simply as surreal. so it was for both of these families. their tragedies were tangled in one riveting mystery that

captain separat captivated the nation. two puzzling deaths and lingering suspicions. the search for the truth would pit the families against each other in a battle sparking more questions than answers. here's josh mankiewicz with "the mansion on ocean boulevard." >> reporter: some places feel secluded. insulated. secure. >> i can remember saying that and feeling that and saying, "nothing bad could ever happen here." >> reporter: "here" is coronado, california, just over a bridge from san diego. a town of beautiful beaches, people and homes. like this one on ocean boulevard. except that in the summer of 2011, this mansion has been ground zero for a mystery. >> this is a very bizarre death. there's no doubt about it. >> reporter: well, actually, there's been plenty of doubt. and plenty of theories. >> my sister was dead.

and did a lot of thing go through my mind? yes. >> reporter: secrets both suspected and imagined. >> is it possible that other people know more than they're saying? yes. >> reporter: it's certainly possible. beyond that, it's hard to say for sure. especially when it seems everyone has a story to tell. and those stories lead to accusations. often with zero proof. >> people are going to believe what they want to believe with no evidence. >> reporter: paradise valley, arizona, was home for the shacknai family. but the summers they spent in coronado were special for dina and her son max. >> max loved the beach. he loved the water. and he used to tell me on the way to coronado, "mommy, this is our place." >> reporter: she and max's dad, jonah, met in 1997. >> we had an instant connection. it's very rare you meet someone like that. >> reporter: they married in 2001, a second marriage for

jonah who was already the father of two. he'd gotten rich owning a pharmaceutical company called medicis. she went back to school to get a ph.d in developmental psychology. and then along came max. >> and then along came maxie. >> he's almost to the edge. oh, my. he did it. how do you feel, max shacknai? >> reporter: he was an active kid who loved sports and performing for his mother and her camera. >> mom, this is my song, right? >> it is, yeah. >> reporter: during one of those summers in coronado, the mansion on ocean boulevard was on the market. >> and i said, "well, let's just go by and look." >> reporter: they bought it in 2007. but soon there was trouble in paradise and a bitter divorce in 2009, when max was 4. they shared custody and worked to be civil. and it wasn't long before jonah

met someone new. >> maxie told me about it. and i said, "wow, well, maybe i should meet her." and he said, "that would be great, mommy." >> reporter: rebecca zahau was 32, born in myanmar. she had moved to the u.s. in her 20s. you were okay with her spending time with max? >> well, max said he had feelings for her. he liked her. at that time, i had no concerns because i trusted that jonah -- based on our history, max would be safe there. >> reporter: and safe in coronado, where nothing bad is supposed to happen. >> tell the operator what's going on. >> hello, um -- >> reporter: july 11th, 2011. max was staying with his dad and rebecca. dina was in coronado too, at a home just down the street. that's when jonah called her. >> and he said, "dina, you've gotta get here right away." >> reporter: as rebecca explained it to police, jonah had been at the gym. 6-year-old max was home with her. rebecca said she heard a crash and found max on the floor near

the staircase. the mansion's heavy chandelier had fallen to the floor next to him. rebecca said max wasn't breathing, and she started cpr. rebecca's 13-year old sister xena, who was visiting, called 911. >> my sister's trying to resuscitate a -- a -- um, a boy. >> i'm sorry -- she? >> he can't breathe. >> reporter: police and paramedics arrived within minutes. jonah called dina from the hospital. >> and he tells me, "thank god that she was able to give him cpr." i think to myself, "thank -- my god." >> reporter: he's gonna be okay? >> he's -- he's gonna be okay. >> reporter: max was unconscious. dina and jonah took up a vigil at the hospital. jonah's brother adam flew in from his home in tennessee. you came out to support jonah? >> correct. >> reporter: how well had you known max? >> i knew max well. he was a really wonderful kid. >> reporter: at max's bedside, jonah asked one of the doctors

for his prognosis. >> dr. peterson looked at him and said, "well, i don't know. i don't know. i'm not sure if he's gonna walk or talk." >> reporter: that sounds like about the worst news you can get. >> but it wasn't real. i would've bet my life on it at that time that max was gonna be okay. >> reporter: there was more bad news on the way. >> 911 emergency. what are you reporting? >> yeah, uh, i got a girl -- hung herself in the guest house. >> what had happened in that house? police uncover some disturbing clues. coming up -- >> they located a female on the property. the victim's hands and feet were bound. >> i guarantee you, my heart started racing. >> who was this victim? >> okay, how old is she? >> i'd say about 30. >> 30, okay. when was the last time you saw her? >> last night. >> soon detectives would be investigating not just one puzzling death here, but two. >> it was the worst shock in probably my entire life.

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>> reporter: the early morning hours of july 13th, 2011. as family members kept a vigil by the hospital bed of 6-year-old max shacknai, a breathless man called 911. >> 911 emergency. what are you reporting? >> yeah, uh, i got a girl -- hung herself.

>> reporter: once again, police raced through the streets of quiet coronado island. and once again, their destination was the mansion on ocean boulevard. jonah's girlfriend rebecca was staying there. jonah's brother adam had spent the night in the guest house. >> you wake up. you walk out. tell me what you see. >> a woman hanging. at the time, i didn't necessarily think to myself, "oh, my goodness, she's bound," or whatever. but just rebecca's hanging. >> reporter: naked, bound hand and foot, rebecca zahau was hanging by the neck from a second-floor balcony. >> i said i guarantee you, my heart started racing. this is actually happening. >> okay. how old is she? >> i'd say about 30. >> 30? okay. when was the last time you saw her? >> last night. >> reporter: even as he called 911, adam says he thought she was dead.

but you try to do something? >> i try to do something. absolutely. and it was not -- never even occurred to me that somebody would look at this as, like, a -- you know, a crime scene or something like that. i mean, that was the furthest thing from my mind and -- >> reporter: so you -- you -- you cut her body down? >> yeah. >> reporter: and? >> started cpr. >> reporter: to no avail. >> to no avail. >> when the coronado units arrived at the scene, they located a female on the property who appeared to be deceased. >> reporter: rebecca's sister mary zahau-loehner was hundreds of miles away in missouri when her husband doug came to her work to bring her the awful news. >> i remember him saying, "rebecca's gone." and i said, "what do you mean? i just talked to her last night." >> reporter: in that phone call, rebecca told her sister about what happened to max. it was the same story she told police. >> she said she was in the

bathroom and she heard a loud noise, a loud crash, and when she came out max was there on the floor. and the chandelier was close to him, and he was unconscious. >> reporter: how did she describe jonah during those days? >> that he was upset and it broke her heart to see him upset. >> reporter: they'd met when rebecca worked for an eye doctor and jonah was a patient. he came in for an appointment and they started talking, and next thing you know, they're going out. >> apparently, yes. >> reporter: you are making an expression that makes me think that you thought that wasn't a particularly good idea. >> i never approved of the relationship, if that's what you're asking me. >> reporter: because? >> first of all, he is almost twice her age. >> reporter: her free-spirited sister fell for jonah anyway. they seem happy? they seem in love? >> i think my sister loved him in her way. to her, she was somewhat in awe of him. i think to a certain extent. >> reporter: mary says that while rebecca and max were

close, rebecca gave the impression she didn't get along well with max's mom. and when max had his fall, mary said rebecca worried how dina would react. >> she was upset about it. and she said, "dina is going to kill me." >> reporter: she said, "dina's gonna kill me"? >> that's correct. >> reporter: rebecca seemed upset, stressed? you get any sense that she blamed herself for what had happened? >> she seemed stressed but not inappropriately so. >> reporter: 'cause everybody was stressed? >> everybody was stressed. and i actually sympathized with her, maybe even mentioned that, of just, "it's gotta be, you know, tough on you. how terrible." >> reporter: soon rebecca's death became national news, in large part because of details revealed by sheriff's investigators. >> the victim's hands and feet were bound, and she was completely nude. it has yet to be determined if this will become a criminal matter or will remain as a death investigation.

>> reporter: in other words, did rebecca hang herself, or was someone else involved? a neighbor reported hearing screams the night before. was that rebecca? there was a scream that somebody heard. you hear that? >> well, my windows were closed. i did not hear a scream. >> reporter: meanwhile, at the hospital, dina says she was only focused on max. she kept watch by his bedside, willing him to open his eyes. it was saturday, july 16th, 2011, 5 days after max's fall. >> and i noticed that his eeg was just flat. and i thought -- i thought the machine was broken. and i'm shaking the machine. and i'm thinking it's not working. it's malfunctioning. i'm shaking. and then i'm saying, you know, "the eeg machine's not working. the eeg's not working." >> reporter: but it was working. 6-year-old max was gone. and dina was devastated. >> i mean, it was the worst

shock in probably my entire life. >> reporter: a mother in shock and in mourning. but also questioning. how exactly had max's fatal fall happened? others asked what led to rebecca's hanging. the mystery at this mansion was only getting deeper. >> coming up -- ropes. knives. a curious phrase at the scene. >> there was a message painted in black paint on the door leading to the room. >> but to some the most curious thing of all? the police theory of what really happened. >> this is a very unusual circumstance. >> we conducted an experiment to determine if it is possible for a person to secure their hands behind their back in the fashion we found. >> when "dateline" continues. here, it all starts with a simple...

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>> reporter: in july 2011, a private funeral was held for 6-year-old max shacknai in arizona. just a few days later, rebecca zahau was laid to rest in missouri. back in coronado, the mansion on ocean boulevard was the focus of overflowing numbers of both questions and rumors. >> there's roughly 200 years of experience in the sheriff's homicide unit. they all agree, this is a very unusual circumstance. >> reporter: rebecca was found

hanging, naked, bound hand and foot. if it was suicide, it looked like a highly unusual one. and remember, rebecca was in the house when max shacknai fell. >> right now, we don't see any connection between the two incidents. >> reporter: the sheriff's department investigated for two months. coronado held its breath. then, at a news conference, sheriff bill gore laid out the facts as his investigators saw them. >> was max's death a homicide? the answer is no. it was a tragic accident. >> was rebecca's death a homicide? again, the answer is no. it was a suicide. >> reporter: sergeant dave nemeth said the evidence told a sad tale, in which one tragedy led to another. when rebecca checked her voicemail just before 1:00 a.m., sergeant nemeth said she heard a grim message from her boyfriend, max's dad, jonah.

>> that message that was left on her phone was to inform rebecca of max's grave condition and imminent death. >> reporter: did rebecca blame herself for the child's severe injuries and then take her own life? the sergeant showed photos from inside the bedroom where rebecca spent her final moments. there was a rope tied to the bed. the other end had been looped around rebecca's neck. there were also two knives in the bedroom, apparently used to cut the rope. everything was swabbed for dna. >> dna profiles were only from rebecca. >> reporter: so what about rebecca's hands and feet being tied? didn't that show another person was involved? sergeant nemeth said it did not. >> we conducted an experiment to determine if it is possible for a person to secure their hands behind their back in the fashion we found. >> reporter: they even showed a video demonstration.

and while tying one's hands in a suicide is uncommon, the medical examiner said it's not unheard of. >> people do it, the thinking is that they bind themselves so that they won't change their mind midway through. it's unusual at first glance, but it does happen. >> reporter: the location of the apparent suicide note, was also uncommon. >> there was a message, painted in black paint on the door leading to the room. i am going to show you a picture of the door. we will not be revealing what the message said. >> reporter: the investigation left some people unsatisfied, none more so than rebecca's family. >> i know in my heart she did not commit suicide. >> reporter: also unsatisfied, dina shacknai. sheriff's investigators illustrated their findings with this graphic. they said max was riding his scooter on the second floor landing, somehow fell over the railing, then hit or grabbed the chandelier and took it down with him. >> that sounds to me like is max some sort of -- you know, a stunt man, bruce lee?

that's ridiculous. >> reporter: why is that ridiculous? he's 6 years old. kids that age do crazy things. when i was 7 years old, i jumped off the roof of the garage holding an umbrella as a parachute. >> no. no. i'm absolutely positive. he was a very smart 6-year-old. he was very athletic. he was very coordinated. and he was a very careful person -- a thoughtful person. >> reporter: dina didn't just insist something wasn't right. she opened her checkbook and hired her own experts, including dr. judy melinek, a respected forensic pathologist who reviewed the autopsy report and photos, and who also disagreed with the official conclusion. >> max had too many injuries to be explained with a simple accidental fall. >> reporter: dr. melinek thought max's injuries indicated he'd been assaulted before he fell. what's more, she questioned whether the fall itself could have happened as the sheriff's department described it. measurements showed the railing

was 32 inches high. 6-year-old max was only 45 inches tall. >> his center of gravity was too low. even on the razor scooter, his center of gravity's too low to go over that bannister. >> reporter: it all pointed to a chilling, alternate scenario. according to dr. melinek, someone assaulted max, and then he somehow went over the bannister. in other words, this was a homicide. >> i would much rather have them say, "you know what? this was an accident. and here's why." no mom wants to hear that her son was a victim of a homicide. >> reporter: and if someone killed max, dr. melinek's theory focused on one person. >> i think rebecca was somehow involved, but how much she was involved and to what degree, she took that to the grave. >> reporter: that alarming suspicion was only the beginning because it wasn't just dina who was investigating. rebecca's sister mary was equally convinced rebecca would never hurt max or kill herself out of guilt.

two women coping with terrible tragedies, neither willing to accept the sheriff's department's conclusions. mary was about to make some incredible accusations and she wouldn't back down. >> could rebecca have been killed? a second autopsy magnifies the mystery. coming up -- >> some deep bruising and internal bleeding which couldn't be explained by hanging. >> reporter: but could be explained by what? >> by somebody knocking her down from behind and hog tying her. something along those lines. a struggle. >> a twist was coming. >> reporter: did you have anything to do with rebecca's death? >> absolutely not. >> you thought you had nothing to hide. >> i knew i had nothing to hide. >> when "dateline" continues.

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i'm dara brown. our top story, president trump reversed course in the wake of withering criticism announcing that the 2020 g7 summit will not

be held at his doral, florida, golf resort. the president says they'll search for a new site. senior u.s. officials told nbc news on saturday that the cease-fire in the turkish area border is not holding. while smoke could be seen rising. the embassy in turkey insisted there are no major violations by the turks. now back to "dateline." welcome back to "dateline." police are ruled 6-year-old maximum shacknai's fatal fall an accident. and rebecca's hanging a suicide. but neither max's mom nor rebecca's sister were convinced. each woman suspected foul play. and one of them was about to make an explosive accusation. continuing with our story, here's josh mankiewicz with the mansion on ocean boulevard.

>> reporter: the official investigation was over. the crime scene tape and evidence markers long gone. that said, an unofficial search for clues was just beginning. online message boards buzzed with theories from the farfetched to the implausible. through it all rebecca's sister mary didn't buy the official finding of suicide. was she fragile? was she easily upset? is she the kind of person that would fall apart after a crisis? >> not at all. >> reporter: so when detectives said that voicemail, the one jonah shacknai left for rebecca with the grim news about max, may have caused rebecca to hang herself, mary wasn't having it. >> i was not about to have my sister's name smeared and the world remember her as this crazy woman who committed her suicide because of a phone call. >> reporter: was all this just about how rebecca would be remembered? after her death came some

revelations, things even mary hadn't known about. like in 2005 in california, when rebecca didn't show up for work and just vanished, her boyfriend reported her missing to the local police department. rebecca turned up a few days later, saying it was just a misunderstanding. >> reporter: you're persuaded that if she did sort of mysteriously disappear back then for a day or two, it was something that she willingly did, and not some sign of mental fragility? >> i really don't know what happened at that time. >> reporter: now she said she needed to know how rebecca died. she had rebecca's body exhumed. and media friendly forensic pathologist dr. cyril wecht then performed a second autopsy. his conclusion, homicide. was rebecca murdered? her family thought so. and eventually, the case found its way to this man. >> it was intriguing from the beginning.

>> reporter: san diego attorney keith greer. >> dr. wecht did identify some deep bruising and internal bleeding, which couldn't be explained by the hanging. >> reporter: wait one second. it couldn't be explained by the hanging but could be explained by what? >> by somebody knocking her down from behind and hog-tying her. something along those lines. a struggle. a struggle. >> reporter: plus, greer says, the force of falling nine feet from the balcony should have caused more severe injuries to rebecca's neck. greer, like dr. wecht, believed someone killed rebecca and then placed her body at the end of the rope. and he began to develop a theory as to who. >> the writing on the door is the key to the case. >> reporter: remember the message painted on the bedroom door? sheriff's investigators initially declined to reveal what it said. greer eventually found out. the message, scrawled in black acrylic paint, read, "she saved him, can you save her?" greer believed the message was

not written by rebecca, it was written about her. >> reporter: who'd she save? she didn't save max. >> she saved max. she did save max. at the time. you have to look at this in context. >> reporter: remember, rebecca said she did cpr on max after he fell. >> reporter: so at the time, those words were written, max was still alive. >> max was alive. >> reporter: and maybe because of her efforts. >> it wasn't maybe because of her efforts. it was exactly because of her efforts and that's why it's the key to the case because i know whoever committed the murder knew that rebecca had saved max. >> reporter: it was, he said, a small circle. mostly family. >> i had an eyewitness who put dina shacknai at the scene of the murder that evening. >> reporter: dina, the grief stricken mom. could she have blamed rebecca and then sought revenge? remember, mary recalled her sister saying, "dina's going to kill me." >> reporter: where were you when rebecca zahau died? >> i don't know what time

rebecca zahau died during that time, but i was at the hospital all night. >> reporter: in 2013, keith greer filed a civil wrongful death lawsuit on behalf of the zahau family. based on his eyewitness, he named dina as a defendant, along with her twin sister, nina. there was also a third defendant. the man who called 911, jonah's brother, adam shacknai. >> reporter: did you have anything to do with rebecca's death? >> absolutely not. >> reporter: greer disagreed. he pointed to those knots tied around rebecca's wrists and ankles. >> figuring them out in the first place is really hard. tying them, almost impossible. >> reporter: greer believed whoever tied the knots had to be an expert, possibly a sailor. and adam shacknai worked on the mississippi river as a tugboat captain. >> when he ties things off, he uses a figure eight and then

closes it with a single hitch or two. guess what knots are tied on both her legs and her hands? figure eights tied off with a single hitch or two. >> reporter: sheriff's investigators had questioned adam extensively after rebecca's death. >> reporter: you didn't hold anything back from investigators? >> nothing. >> reporter: you helped them to the extent that you could. >> yeah, exhaustively. >> reporter: you thought you had nothing to hide. >> i knew i had nothing to hide. >> reporter: and when investigators determined there was no evidence placing adam at the scene -- >> reporter: they cleared you. >> they did. >> reporter: did you think this was over at that point? >> yeah, i did. >> reporter: it wasn't over. rebecca's sister was determined to hold someone accountable. >> reporter: i'm guessing that somebody said to you that filing a lawsuit, a civil lawsuit, to find answers in a criminal matter is generally an extremely unsatisfying way of pursuing justice.

>> that may be, but my only recourse was the lawsuit. >> reporter: soon they would start to get answers, just not the ones they expected. >> reporter: coming up, where was dina the night of rebecca's death? >> this eyewitness was adamant, she was very clear, no doubt about it. >> powerful new video evidence. and the dna evidence, where was it? >> adam shacknai admits he cut rebecca down that morning. he loosened the ropes on her wrist to check pulse. he gave her mouth-to-mouth resuscitation. >> and there's no dna. >> zero. >> when "dateline" continues. so...magic mornings happen. there's a better choice. aleve pm.

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>> reporter: seven years after the death of her son max, dina shacknai lives alone in the arizona home she once shared with her family. how are you even standing upright today? >> max, my son. my love for him was so great. we were a perfect fit. we were lucky. i still feel lucky. >> reporter: even though he's gone? >> yeah. >> reporter: in the years following max's death, dina continued to investigate and hired a woman named tara schneider. you're convinced that max died not as the result of an accident but a murder. >> yes. homicide. >> reporter: tara has no law enforcement background. she calls herself an

intelligence analyst. she and dina have floated several theories over the years. the current theory -- whoever killed max, it was not rebecca zahau. these days their suspicion is focused on information from a neighbor that's never been verified. a story of a wild party at the mansion the night before max's fall. >> he has not been interviewed by the police and he has not come forward. >> reporter: but what connection it might have to max's death, you have no idea what that is. >> i don't. but i think it should be explored. >> reporter: she said police never spoke with the neighbor. but we did. and he doesn't remember anything about a party. and max's dad jonah shacknai, who was in the house that night, told us there was no party. jonah says he never doubted the official investigation, but wanted to rebut the theories offered by dina and others. his lawyers hired the highly regarded investigative firm kroll.

the resulting report says, "the evidence is consistent with an accidental, tragic fall, and there is no evidence of foul play, malice or other non-accidental occurrence." how many people said to you, "you need to let this go and move on"? >> many. so many. >> reporter: even if she'd wanted to move on, it really wasn't possible because dina, remember, was being sued by the family of rebecca zahau, who blamed dina in part for rebecca's death. through it all, dina stuck to her story, that she'd been at max's bedside at the hospital the night rebecca died. even though the zahau's attorney keith greer had an eyewitness willing to testify that he saw dina outside the mansion that night. >> and this eyewitness was adamant. he was very clear. no doubt about it. >> reporter: and turned out to be dead bang wrong. >> and turned out to be wrong. >> reporter: in april 2017, after four years of litigation,

this security camera video came to light. it's from the hospital where max shacknai was being treated the same night rebecca zahau died. clearly visible -- dina shacknai. at some point you look at the footage from the hospital and you realize, "i'm wrong and my witness is wrong. dina wasn't there. she was at the hospital provably." >> absolutely. i got mad. i got really mad. >> reporter: greer called a press conference to publicly eat some crow. >> when these pictures come out, though, you can't refute 'em. >> reporter: he removed dina from the lawsuit, along with her sister nina. and the zahau family attorney apologized to you. was that enough? >> he made a public apology. and i would say that not as many people saw the public apology as who saw continuous accusations against us. >> reporter: greer pushed forward anyway with just one defendant -- adam shacknai. that says to me this is some scattershot attempt and you are suing everybody that comes into

your line of sight looking for a sympathetic jury. >> that's it. and a lot of people looked at it that way. >> reporter: why shouldn't that shatter the credibility of the rest of your case? >> i think the reality of it is that we always had adam involved all through the process. >> reporter: in the lawsuit, greer outlined quite a detailed and unsubstantiated narrative. he argued rebecca was killed not to avenge max, but instead, during a sexual assault. greer's theory is that it began when rebecca stepped out of the shower and found adam in her bedroom watching her. >> she then gets uncomfortable and tries to escape. she screams for help about 11:30 that night. >> reporter: greer says that explains the screams heard by a neighbor. >> right after that, to silence her, adam hits her on the back of the head, knocks her at least partially unconscious. then he has time to think and he grabs the black paint and he paints this phrase on the door. "she saved him. can you save her?"

>> reporter: if i'm gonna kill somebody and try to make it look like a suicide, i'm not gonna write a cryptic phrase behind. i'm gonna write a phrase that says, "i'm sorry. i'm guilty. i did it." >> yeah. it wasn't staged to be a suicide. >> reporter: even greer says evidence placing adam at the scene is weak. adam shacknai have any marks or scrapes or cuts on him that would suggest he'd been in a struggle with someone? >> none. none. >> reporter: same with adam's dna. it's pretty hard to get rid of your dna. >> hard to get rid of dna. all right? adam shacknai admits that that morning he cut rebecca down. he loosened the ropes on her wrist to check her pulse. he gave her mouth-to-mouth resuscitation. he gave cpr pumps to her chest. >> reporter: and there's no dna? >> and how much dna and how many fingerprints are found on the knife, the rope, her body, how much? >> reporter: none. >> zero. zero. >> reporter: zero of adam's, that is. rebecca's dna and fingerprints were everywhere.

according to greer, that means adam, who had no criminal history, knew exactly how to wipe down the scene, somehow removing his own fingerprints and dna, but leaving just rebecca's. of course, it could also mean that adam simply wasn't there when rebecca died, which is exactly what law enforcement came to believe. i'm guessing that if you walked in at court on any case and opposing counsel said, "there is no evidence here, and there is no fingerprints, and there is no dna, and that is the proof of the case that i am bringing," you would think to yourself, "i got a groundball here." >> the absence of evidence isn't the evidence of absence. and so we know it's murder 'cause it's wiped down. we know it's not suicide. >> reporter: would a jury agree? greer had to prove adam shacknai was somehow responsible for rebecca's death, that his own actions made him liable.

in a wrongful death civil case, the standard is "more likely than not," a significantly lower bar than "beyond a reasonable doubt," which is the standard in a criminal case. it is, however, still a challenge. and when the case went to trial, keith greer would be up against a top notch defense team. you feel overmatched? >> i was so outgunned, it was pathetic. >> two families connected by tragedy prepare to go head-to-head in a courtroom. coming up -- >> reporter: did you attack her? >> no. >> reporter: did you sexually assault her? >> no. >> reporter: did you tie those knots on her body? >> no. >> would a jury believe him? >> i sat down next to mary, i said, mary, i'm sorry this, is probably not good news. >> when "dateline" continues. with pronamel repair toothpaste, we can help actively repair enamel in its weakened state. it's innovative. with pronamel repair, more minerals are able to enter deep into the enamel's surface.

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welcome back. rebecca's death had been ruled a suicide but her sister mary was convinced she'd been murdered by adam shacknai. adam insisted he tried to save rebecca after typing her hanging from a balcony. now the two were facing off in a civil lawsuit. a jury would decide who was responsible for rebecca's death and the verdict would leave both sides stunned. here's josh mankiewicz with the conclusion of "the mansion on ocean boulevard." >> the plaintiff's attorney got -- he's got a good imagination. >> reporter: adam shacknai says it's simple. he had nothing to do with the death of rebecca zahau. were you present when rebecca died?

>> no. >> reporter: did you attack her? >> no. >> reporter: did you sexually assault her? >> no. >> reporter: did you tie those knots on her body? >> no. >> reporter: are those the kind of knots that only a sailor or somebody who worked around boats in the water would know? >> no, those are common knots. >> reporter: sheriff's investigators found no evidence adam was present when rebecca died, and they cleared him. that didn't stop rebecca's family from suing in civil court. >> the lawsuit. the long string of accusations. what do you think's going on here? >> it's denial. it's -- they don't wanna be seen that their sister committed suicide. >> reporter: we asked rebecca's sister mary about that. a lot of times families do not want to admit that someone committed suicide because they blame themselves for not maybe having seen the signs. is that what you're doing here? >> no. and i have been accused of that multiple times, including the sheriff's department.

>> reporter: is it possible that rebecca was depressed and you missed it? >> no. >> reporter: in march 2018, the wrongful death lawsuit began in san diego. defending adam was dan webb, a former u.s. attorney and a veteran of many courtrooms. >> there will be no evidence that shows that adam shacknai had anything to do with the death of rebecca zahau. >> reporter: in particular, no dna or fingerprints from adam were found at the death scene. plaintiff's attorney keith greer called several experts who testified that the lack of physical evidence could show adam had cleaned up after himself. doorknobs whatsoever as far as prints. >> and that was consistent with it being wiped down? >> yes. >> reporter: and a handwriting expert who looked at that message on the door. >> the writing on the door more comports with adam than it does with rebecca. >> reporter: greer also claimed rebecca had been sexually

assaulted with a knife prior to her murder. his expert testified a steak knife found in the bedroom had her blood on the handle. greer said the sheriff department overlooked that evidence. >> that's nowhere on any of the sheriff's records. they never considered that. they never analyzed that. >> reporter: the defense called a forensic technician who testified she did find the blood on the knife and with it, a simple explanation. a recent cut on rebecca's right hand. and when greer asked her if the blood could have come from a sexual assault. >> i didn't see any evidence of that. >> reporter: no evidence. a point the defense hammered home. >> i saw no fingerprint evidence that was identified or directed towards adam shacknai. >> of all the items i tested, he was excluded on all of the items. >> reporter: adam's brother jonah took the stand. he called rebecca's death "unfathomable," but said adam was not responsible. >> is there anything that adam's ever done in his life that would

cause you to believe that he ever would have done the acts that he's accused of in this case? >> never anything. it's inconceivable. >> reporter: adam took the stand too. >> did you hit rebecca on the head? >> i never hit rebecca on the head or anywhere else for that matter. >> and did you devise this scheme to try and cover up your wrongdoing by painting this saying on the door and making it look like she had been hanged by someone else? >> absolutely, positively not. >> reporter: the case went to the jury. did you feel confident as deliberations began? >> i felt we could possibly win very convincingly. >> reporter: less than four hours later, a verdict. >> i sat down next to mary and i said, "mary, i'm sorry. this is probably not good news." >> reporter: this was it. a decision. and even keith greer would be in for quite a plot twist. >> number one, did adam shacknai touch rebecca zahau before rebecca zahau's death with the

intent to harm her? the answer is yes. number two, did that touching cause the death of rebecca zahau? the answer is yes. >> reporter: yes, meaning that the jury found adam shacknai responsible for rebecca zahau's death. >> i just broke down. i was just like, "okay. i'm not crazy. i'm not the only one who believes that adam murdered my sister." >> reporter: that's not quite what the jury said. finding someone liable in a civil case is not the same as finding them guilty of murder. what's more, the verdict in this case did not have to be unanimous, and it wasn't. nine jurors found adam responsible. three did not. the jury did award the zahau family $5 million. courtrooms are supposed to be a place where justice is dispensed. was this about justice? >> no, it wasn't.

>> reporter: since this wasn't a criminal case, adam didn't go to jail. he returned home to tennessee. he filed a motion for a new trial which was denied in january 2019. thin in february adam a insurance company and rebecca's family reached a settlement of $600,000. and the case was dismissed. after the civil trial, the sheriff's department took a fresh look at rebecca's death. eight months later that concluded rebecca died by suicide. dina would like to see authorities reinvestigate her son's case. do you think they will reinvestigate max's death? >> i think it's the right thing to do. do i think it will happen? i really don't know. >> how does a mother ever truly accept the tragic loss of a child? the ripples keep on spreading to this day in a place where nothing bad was supposed to

happen. >> that's all for in edition of "dateline." i'm natalie morales. thank you for watching. of "dateline." thank you for watching. i'm craig melvin. >> i'm natalie morales. >> and this is "dateline." >> how am i doing right now? if i had to put it into one word, numb would be the closest. >> she was a young actress starring in a role of a lifetime, a mystery. >> you never heard a gunshot? >> no. >> one of her friends was dead. >> there has been a body discovered in sam's apartment. >> it's so hard. she was 23. >> another friend was missing and wanted. >> you got a dead woman in his apartment. this guy is potentially very dangerous. >> we were pretty confident he was our