. tonight, our "20/20" investigation. >> you would have to throw yourself over head first bound and gagged. >> why would a young woman tie herself up like this before hanging herself? >> who does that? i'll tell you who does that, nobody. >> the police say she did in a baffling case that made national headlines. >> was found naked and hanging. >> part of a book by crime writer, ann rule in civil court just this week. >> i never wanted to investigate my sister's death to find out the truth. >> tonight, all the new developments in the mystery involving a well-known millionaire. >> welcome back to the show. >> and the suspicious show. an historic water front mansion. >> there was a dead body, a

woman found nude hoanging off a balcony. everybody was all over it. >> especially when they heard rumors of witchcraft. >> i said, what? my girlfriend, whom i loved is dead. it was surreal. >> and the millionaire's brother who found her body. >> does it seem to you like it's a suicide? >> yes, absolutely. >> but when authorities rule it case closed -- >> they treated my sister like garbage. >> "20/20" has their own investigation. >> and you have to take one more hop. >> giving the family answers they can accept. was there suicide? >> it was a muystery. >> let's get the answers. >> i'm david muir, and this is "20/20." you're about to see this fascinating investigation tonight with abc's sunny hostin, a former prosecutor herself. we begin with the words of true

crime writer, ann rule. >> the dark-haired woman was beautiful, even in death, and the moonlight dappled her naked body. her name was rebecca, the girlfriend of pharmaceutical tycoon jonah shacknai. she was 32. the way rebecca zahau died was strange enough. >> it was almost like a movie. you can't make this stuff up. >> reporter: but where it happened made it all the more bizarre. >> having something like this happen in coronado was just so shocking. >> coronado's really an island with a bridge coming out of san diego. you're right on the ocean. and then there's these mansions, one after another, after another. >> reporter: and of all the beautiful spots in coronado, the body was discovered at one of the most historic, the spreckels mansion. >> spreckels mansion was named after a sugar king! spreckels mansion has so many bedrooms you can hardly count them. grand staircases.

you don't really think of a dead body hanging off the balcony when you ride by. >> reporter: rebecca zahau came a very long way to end up dead in coronado. her family was royalty in a remote part of a remote land. the country once known as burma. >> she was funny. she could always relate to anybody. if rebecca walks into the room, everybody remembers rebecca was there. >> reporter: after the family was forced to flee their homeland, rebecca ended up nearly 10,000 miles away in america. >> she was very excited to come to the u.s. she was very, very excited about starting a new life. and then she found it. >> reporter: part of that new life, her job in an ophthalmology office. >> she was an ophthalmology tech. it's anywhere from grooming people to getting ready for surgery. like cataract surgery. any eye surgeries.

>> reporter: did she like that? >> oh she loved her job! >> reporter: one day a patient came in whose eyes worked plenty well enough to notice the beautiful technician. his name, jonah shacknai. >> rebecca was completely full of life. she was a very enthusiastic person. >> reporter: rebecca had no idea what a catch she just attracted. >> jonah shacknai was absolutely loaded. this is the guy behind medicis pharmaceutical, which is the coca-cola of the medical cosmetics industry. a company ultimately worth billions of dollars. >> jonah, welcome back to the show. >> thanks, great to be here jim. >> reporter: shacknai was a star in the business world, known for his innovative products. >> medicis pharmaceutical found the holy grail, they figured out how to create something similar to botox. >> reporter: but when he met rebecca, he says the attraction was much more than skin deep. >> we both loved to be outdoors, we were both workout enthusiasts. we both like clean living, clean food and things like that. just made it very compatible on a daily basis.

>> reporter: the more he learned about rebecca's past, what she went through escaping burma, the more she fascinated him. >> i just had enormous admiration for her. just because they were running and trying to find a place, to have a stable life. >> reporter: now, it was as if rebecca had stumbled upon prince charming. but some say their life together was no fairy tale. >> rebecca zahau's family was not keen on the relationship. there was no ring on her finger! he already had several children! >> reporter: two teenagers from his first marriage, and a little boy named max from his second. >> max loved rebecca. she was extremely attentive and warm. and she had no children of her own. and i think she was a great influence on max. they had their own love story. >> there was friction between dina shacknai and rebecca. >> dina wasn't crazy about the

new girlfriend moving in on her 6-year-old son. >> when you have blended families, you want -- i mean no mom is jumping for joy saying, "oh, somebody else is gonna be, you know --" >> reporter: around your child. >> i thought we had a good working relationship together. >> reporter: what was dina's relationship with rebecca? >> it was not a friendly relationship. it was not friendly at all. >> reporter: did you approve of the time she spent with max? >> yeah, i didn't disapprove of it. in fact, i would expect it, which is the reason that i wanted to meet her so that she and i would have a good relationship so that max would feel like it was okay. >> they were not close. i think there were times when dina made it a bit difficult for rebecca. >> reporter: but no one could have imagined just how difficult things were about to become. >> it was july the 11th. it was in the morning. >> reporter: jonah shacknai had already gone to work out at a nearby gym. >> and rebecca was in the house

with her little sister xena. >> she happened to be visiting. xena is in one part of the home. rebecca is in another part of the home. max is on the second floor and he's playing. >> reporter: when something awful happened. >> 911, what is your emergency? >> reporter: rebecca's sister xena called 911. >> he fell down the stairs, he's not breathing. >> reporter: somehow 6-year-old max had taken a horrific fall, which neither rebecca nor xena saw. rebecca called jonah. >> i literally sprinted into the house and saw max laying on the floor. >> when i first saw him. he had tubes coming out of every, you know, orifice of his body. for any parent to see your son like that, i was just like, wow. >> reporter: did she ever tell you how he had the accident? >> i said, "what happened," and she said, "i really don't know. when i came out he was there on the floor." she's like, "dina is gonna kill me."

and i said, "what do you mean?" she's like "she's gonna kill me." and she kind of repeated it several times. >> reporter: during the family emergency, the parents held vigil by max's bedside. and the next day jonah's brother adam flew in from tennessee. >> adam came to be with us and to be of whatever support he could. anyone that's had a child with a grave injury understands it's the loneliest place on earth. >> adam shacknai was in the guesthouse. rebecca was at home. those were the only two in the house. >> they weren't that well known to one another, but they were exceedingly cordial. both good people that i think had all eyes and prayers on max. >> reporter: but a bad situation was about to get worse. >> 911 emergency what are you reporting? >> i got a girl hung herself. >> is she still alive? >> i don't think so. >> she was dead. >> her body was found

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most murder victims know their killers. and so superior detectives look first for connections, the interweaving of lives that may have led to homicide. >> reporter: wednesday, july 13, 2011. as the sun rises over coronado, adam shacknai walks into a scene of horror at the spreckels mansion.

>> adam was the one who came out of the guesthouse sometime after 6:30. and he saw rebecca's body hanging from the balcony. he called 911. >> what's your emergency? >> yeah, uh, i got a girl, hung herself. it's on ocean boulevard across from the hotel. same place that you came and got the kid yesterday. >> okay, sir, is she still alive? >> i don't know. >> sir, are you there? >> are you alive? no! >> reporter: adam is able to cut rebecca's body down and he desperately tries to resuscitate her. >> is she beyond help? >> i'm compressing her chest right now. >> okay, hold on. listen to me. help is coming right now, okay? >> reporter: but by the time help does arrive, it's already too late. rebecca zahau is dead.

her boyfriend jonah shacknai is at the hospital where his son max is in critical condition. he receives an urgent text from his brother adam to call him. >> and he told me that rebecca had taken her life. and i said, "what?" can you imagine the impact of something like that when i was already facing, you know, certainly the biggest crisis of my life? so yeah, it was surreal. >> reporter: but if rebecca had taken her own life, it would be a truly puzzling way to commit suicide as seen in graphic police photos. >> no woman would bind their feet with rope, bind their hands behind their back, put a t-shirt around their neck, gag it in their mouth, and then jump over a balcony. >> anybody that looks at this says this could not be a suicide. that's just impossible. >> 32-year-old rebecca zahau was found -- >> bound and hanging from a

balcony. >> reporter: news of the bizarre death at the famous mansion spreads like wildfire. >> as soon as we heard there was a dead body -- a woman found nude hanging off a balcony off the spreckels mansion, oh, my goodness, everybody was all over it. >> 6-year-old max has died due to complications due to falling inside the home. >> reporter: and the story becomes even more tragic when just three days after rebecca's death. max dies in the hospital. >> i miss his presence, i miss his wisdom, his laughter, his love. i miss watching him grow up. >> reporter: with two mysterious deaths in the same house in the space of a few days, the san diego sheriff's department launches a full investigation. >> the scene was pretty suspicious. we're not ready to determine whether it was a suicide or a criminal act. >> reporter: "20/20" was able to obtain a copy of the sheriff's department's investigation into rebecca's death. and it raises a number of questions. rebecca's room is shrouded in

mystery. one end of the red rope that she was hung with is tied to her bed. the other end leads out to the balcony, where her footprints are found as well as a man's boot print. detectives note a curious book found on a shelf. "buckland's complete book of witchcraft." as part of a rite, it shows drawings of a naked woman with her hands tied behind her back and mentions that "red cord" should be used. >> they would say, "well, maybe she was into some things that were, you know, of the occult, or kinky," things like that. >> reporter: perhaps the biggest enigma of all is found right on rebecca's door. a cryptic message scrawled in black paint. "she saved him, can you save her?" >> nobody could figure out what it meant. it didn't really make any sense, because we didn't know who he or she were. >> reporter: suspicions of a possible homicide ratchet up when a neighbor comes forward, telling police she heard desperate screams coming from

the direction of the mansion that night. >> i heard the woman yell, and then yell for help. she went "ah, ah!" and then she went "help, help!" >> reporter: suspicion by investigators immediately falls on adam shacknai, the only one staying at spreckels with rebecca at the time. to remove suspicion, shacknai agrees to take a police lie detector test the very day he found rebecca's body. >> regarding the death of rebecca, did you yourself do anything to her that resulted in her death? >> no. >> reporter: shacknai neither passes nor fails the test. >> you could have done a whole lot worse on the test. you could have done a whole lot better, too. based on what i've got here, you're in the inconclusive range, which really doesn't bother me that much. >> reporter: not much is known about the younger brother of millionaire tycoon jonah shacknai. >> i think he definitely has a different personality than jonah. i mean, it probably might be hard to be jonah's brother, but he really has carved out his own

niche. >> i love you uncle adam. >> adam is a very nice guy. he's the captain of a tugboat. he wakes up and his life is changed forever, just because of where he was. the wrong place at the wrong time. >> reporter: but what about ex-wife, dina? remember, rebecca's family talked of tension between her and dina. and after max's accident, police overheard rebecca telling her sister that, "dina's going to kill me." >> dina definitely had a motive. her son died under her ex-husband's girlfriend's watch. >> reporter: adding fuel to the fire, an eyewitness comes forward, telling authorities he saw a woman matching dina's description approach the mansion's front door late the night before rebecca's death. clouds of suspicion over the two deaths at spreckels, now hang heavy in the coronado seaside air.

but as the weeks pass, there are no arrests. >> each day that went by was a day without answers and was frustrating. >> reporter: finally, the sheriff's department calls a press conference to announce that they have solved the mystery. >> were these deaths the results of criminal conduct? >> reporter: coming up, the official cause of death, and why it would enrage rebecca's family. >> they never wanted to investigate my sister's death to find out the truth. >> reporter: but just how far would rebecca's family go to solve the mystery? >> her body was exhumed on television. it's -- it's terrible. >> reporter: when "20/20" continues. no, please, please, oh! ♪ (shrieks in terror) (heavy breathing and snorting) no, no. the running of the bulldogs?

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the very wealthy are not immune to scandal. being rich doesn't assure safety, not at all. sometimes it attracts aberrant minds. >> reporter: months have passed since those two mysterious deaths at the landmark spreckels mansion. first, 6-year-old max shacknai had somehow taken a fatal fall off a second story landing. then just two days later, 32-year-old rebecca zahau was found hanged to death at spreckels under highly suspicious circumstances. >> reporter: detectives this morning are investigating the mysterious death of woman whose nude body was found bound and hanging from the balcony of the historic spreckels mansion. >> reporter: we're told there are no suspects and no one's been ruled out as a suspect. >> people were on pins and needles.

what were the conclusions, what was the cause of death? what happened to max? what happened to rebecca? >> i'd like to introduce sheriff bill gore. >> reporter: finally, seven weeks after rebecca and max's deaths, sheriff bill gore calls a press conference to announce his department has solved the mysteries. >> were these deaths the result of criminal conduct? was max's death a homicide? the answer is no. was rebecca's death a homicide? again, the answer is no. >> reporter: gore and his team lay out their findings. max's death, they say, was the result of a freak household accident. >> something caused him to trip, whether it was a ball, whether it was the dog, or something that he then tripped and fell over that railing grabbing the chandelier. >> reporter: when it came to rebecca's death investigators say it had nothing to do with witchcraft, and certainly not homicide. they say the autopsy and dna and fingerprint analysis showed no signs that rebecca had been attacked.

>> fingerprints from the bed leg directly next to the rope were all from rebecca. dna profiles from the victim's bindings were only from rebecca. >> reporter: investigators would later discount as unreliable the report from that neighbor who said she heard screams for help that night. as for that mysterious male boot print on the balcony, they said it was accidently left by a police officer. investigators say that the fact that only rebecca's footprints were on the balcony confirmed their suicide conclusion. >> toe impressions on the balcony are consistent with a person moving up next to the railing and leaning forward and going over the railing. >> reporter: but if it was suicide how could rebecca have tied her own hands behind her back in such a seemingly intricate way? investigators show this video of how a female officer is able to first tie herself up, then slip one hand out of a noose and put it back in with her hands behind her back.

they conclude that rebecca did the exact same thing. >> just a simple matter of slipping her hand out. the bindings were not tight. >> when they presented their case we were all lookin' at each other like, "really? really?" >> reporter: but of course, there's still the question why -- why would rebecca commit suicide in the first place? investigators say rebecca had been under stress and hit a breaking point after listening to a voicemail message saying just how grave max's condition was. >> i left her a voice message, pretty upset. >> reporter: jonah shacknai says he was the one who left that grim voicemail message for rebecca. >> all i can think is that rebecca saw what had happened, felt responsible in some way, not that she did anything, but that she was entrusted with max. and that that was too much to bear. >> our condolences go to their family. we also would ask because of that, that you allow them to go through the grieving process.

>> reporter: but if law enforcement thought rebecca's family would take their grief and go quietly into the good night, they were dead wrong. >> they treated my sister like garbage. i believe they felt like, they came to a quick conclusion that becky mostly likely had something to do with max's -- and she deserved what she got. >> did you ever believe that your sister was suicidal in any way? >> no. rebecca does not have a suicidal personality at all. >> reporter: rebecca's family turns their outrage over the sheriff's investigation into action. they hire high profile attorney anne bremner who helps them take their case to the media. >> they wanted to get the word out because they were powerless with the police. so they took their message and they put it out to millions of people. >> the cause of death of this millionaire's girlfriend -- >> reporter: rebecca's case is featured on the dr. phil show. one of his guests is dina shacknai, who is also

unhappy with the sheriff's findings. she says an expert she retained concluded that max's death wasn't an accident. >> you believe that this whole scenario of what happened that resulted in max's death is just completely wrong? >> right. max going over the bannister, his center of gravity was too low. and it defied the laws of physics. >> you have really devoted your life to finding out what happened to maxie. >> yes. he was my only son. >> reporter: on another episode, rebecca's family controversially exhumes her body and has renowned forensic pathologist dr. cyril wecht conduct a second autopsy. wecht notes four small hemorrhages on rebecca's scalp that he says could be a possible indicator of foul play. >> i lean very strongly to it being a homicide. >> reporter: the san diego county coroner also found those head wounds, but concluded rebecca's head could have struck

something as she fell from the balcony. >> her body was exhumed on television, on the dr. phil show, disgustingly. it's -- it's terrible. >> he can say it's ghoulish, you know. what we say is it's justice. they know what happened to her, and she didn't kill herself. >> reporter: rebecca's family petitions the california attorney general to re-open rebecca's case. but in a crushing blow -- their request is denied. >> to have it rejected without comment was really, really difficult. anyone that's heard of this case says, "that's not a suicide." let's get the answers. let's get the answers. >> reporter: coming up -- "20/20" enlists this former nypd detective to take a new look at the zahau case. >> it's a mystery. and i don't like mysteries. >> reporter: the results of his investigation, when we return.

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there were things money can never buy, and sometimes it seems that those who have too many in worldly goods pay for it with terrible losses they could not foresee. becky was gone. >> reporter: seven years after the death of rebecca zahau, the mystery lingers. how could this beautiful young woman have committed suicide fully naked, with her feet bound and her hands tied behind her back? >> i think the interest in this case remains years and years and years later. i hope somebody looks at this case again. >> reporter: it turns out someone is re-examining the

case, 3,000 miles away from the sunny beaches in coronado, here in the city that never sleeps -- new york. his name is herman weisberg, and he's a seasoned private investigator in new york city with lots of high profile cases under his belt. weisberg is also a retired veteran nypd detective. "20/20" retained weisberg to do a deep dive into the rebecca zahau case. he examined the case file of the san diego sheriff's department, poring over the detailed investigation. >> it's a mystery. and i don't like mysteries. and this one begs for a bunch of questions to be answered. >> reporter: have you seen anything as perplexing as this one? >> perplexing? no. >> reporter: weisberg says one of his biggest concerns about the san diego investigation was over the forensic analysis.

remember, one reason investigators concluded that rebecca wasn't murdered was because only her fingerprints and dna were found at the scene. >> they say science doesn't lie, that's why i'm so confident here. >> there's a lot of questions about what should have been found and what wasn't found there. >> reporter: for instance, weisberg wondering how it could be possible that there was no trace of adam shacknai's dna and fingerprints, considering that he says he cut down the rope rebecca was hanging from and administered cpr. >> i just put mouth over hers, i said, "-- it, it's my brother's girlfriend, i'll do it," and i did it." >> reporter: is it odd to you that his dna was not found on the rope? was not found on rebecca's body? >> the fact that it's not there means it wasn't collected properly or it wasn't analyzed properly or both. >> reporter: weisberg is also troubled by the investigators' conclusion that rebecca was able to hang herself with her hands tied behind her back. when you look at the way her

hands and her feet were bound, what are your observations? >> this is a very intricate way to bind anyone. looks to me like it takes some knowledge. >> reporter: but remember, the san diego sheriff showed how a woman was able to bind her hands behind her back in way they said was similar to rebecca. >> best we can tell, there was nothing, no particular expertise required. >> reporter: no particular expertise? to find out, weisberg met up with a rope tying expert -- >> nice to meet you. >> pleasure. >> reporter: greg hanchrow, a new york harbor port captain and a former tugboat captain. weisberg showed him the bindings on rebecca's wrists. >> could these be done by somebody like me who's never really had an experience with tying knots for these purposes? >> i don't think a layman that has never secured stuff before would come up with that kind of

lashing and knot to tie it. but it doesn't have to be exclusively from a maritime background. >> let's just take this, and show me how you would do it. >> reporter: just like the woman in the sheriff's video, hanchrow was able to tie his hands behind his back using the same type of rope on rebecca's wrists -- but even he found the process to be awkward. >> so now i'm gonna try to tighten the knot. >> i can't imagine this happening without a lot of practice. this is a very elaborate situation. >> it's pretty elaborate. i would say to a layperson, that's pretty out of the ordinary. when you lay a lashing like that, there's experience behind that. >> reporter: but could rebecca have had that kind of rope tying experience? after all, jonah shacknai says she often went out with him on his boat in coronado. >> rebecca, who was a really good athlete, would sort of jump off the boat and tie it down. certainly she tied down our boat on dozens of occasions.

>> reporter: but our rope-tying expert told us that the type of bindings found on rebecca wouldn't be used to tie down a boat. weisberg also has questions about what the san diego investigators say happened on rebecca's balcony. remember -- they concluded that because only rebecca's footprints were found on the balcony, she must have thrown herself off. to see just how likely that scenario could be, weisberg brought me to this balcony, roughly the same dimensions as the one at spreckels mansion. >> so from this point forward, it's roughly 24 inches or two feet. the rail from balcony, it's right around the same, within an inch. >> reporter: she would have hopped. hopped. >> it's extremely difficult to get yourself in that position while you're tied up, while you're wearing a gag. >> reporter: naked. >> naked. and your ankles are bound. >> reporter: and pretty gruesome, too.

you would have to throw yourself over headfirst, bound and gagged. but could an attacker have thrown rebecca off the balcony without actually stepping on it and leaving incriminating footprints? to find out if that was possible, we brought in this dummy. is this dummy similar dimension? >> similar. a little bit heavier. we erred on the side of heavier rather than lighter. it's a really good way of determining if this is possible for me to do this. >> reporter: all right, let's see if you can do it. so it is possible. >> it's not easy. >> reporter: it's not easy, but it's possible for you to have not stepped out there and positioned the body and thrown the body over. >> sure. it shows that someone could have taken rebecca's body, put it down,

leaned it against that rail and shoved it off. >> reporter: in the end, weisberg says his evaluation raises serious questions about the san diego sheriff's department's findings in the rebecca zahau case. just looking at it with a fresh pair of eyes, does the evidence point to a suicide in your view? >> i'm not completely satisfied that this was a suicide. but there's also not enough evidence at this point to show that this was a homicide. i think there's a lot of evidence that has to be re-examined. i think that we really need a fresh look at what wasn't done here. >> reporter: the san diego sheriff's department declined our request for an interview, but told us they are always willing to look at any new evidence or information that comes to light. coming up, rebecca's family finally has their day in court. >> that was the last time i saw my sister. >> reporter: will this mysterious writing on the door help them win their case?

>> the jury's gonna get to see the truth. >> when "20/20" continues. are cream conditioners bringing your hair down? switch to new pantene light as air foam conditioner, full of rich pro-v nutrients. for 100% conditioning, 0% weight. new pantene. foam conditioner.

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three critericriteria, moti opportunity and ability are considered as suspects in any criminal investigation. who had the desire to kill ms. zahau? who had the opportunity to get close enough to actually cause her harm? >> the theory that i heard the most was that this little boy had this horrible accident, and that, you know, the father's girlfriend was supposed to be looking after him. so the speculation was that this was a revenge killing for what happened to max.

>> reporter: but rebecca's family wanted justice and hired attorne keith greer. several years ago, he filed a wrongful death suit for the family, claiming that dina, her sister nina, and adam conspired together to kill rebecca. >> i had an eye witness who was very convincing, really strongly believed that he saw dina there that night acting suspiciously. >> and they are now filing a wrongful death suit against three members. >> reporter: remember the mysterious woman seen knocking at the mansion door that night? at first, she was identified by that eyewitness as dina. >> we've always alleged that we have evidence we felt put dina and nina at the scene of the incident. >> they accused you of striking rebecca in the head. four times, helping to tie her up, gag her and stage the suicide. >> i think it's a disgraceful

abuse of the legal system. on what planet, in what universe would anyone come up with this kind of scenario? without any scintilla of evidence or facts, nothing. >> reporter: turns out that the woman who knocked on that door that night wasn't dina at all. when this footage revealed that dina was at the hospital with max at the time of rebecca's death, greer dropped both sisters from the civil suit. >> i want to take this opportunity to express a real heartfelt apology to dina and nina. >> so this has had an impact on our career and our reputations. and it's been a really horrible thing. >> reporter: without dina and nina in his sites, greer's case for the zahau family is targeted at adam shacknai alone. >> adam was there overnight and nobody else was. >> you think adam killed your sister? >> yes. i totally believe he did.

it was almost, like, max is hurt and rebecca is responsible. >> reporter: in court filings, greer presented the family's version of what happened to rebecca that night. walk me through what you believe happened to rebecca that night. >> first there was a confrontation. he was in the house, in the room with her. we'll never know exactly what's said or how it escalated. shortly after that, she was hit on the back of the head four times on the right upper part of her head. the next thing the killer did was tie her up. she was strangled before she went over the deck. >> adam's attorney says none of it makes sense. >> reporter: adam says he never left the guesthouse that night. none of his dna or fingerprints was found. but greer claims adam wiped the scene down. how could that be, adam's team asks, if rebecca's prints were found? >> i know he's a really smart guy, and he's a clever guy. and he -- and he put together

this stage bizarre scheme to cover it all up. >> to be the subject of a lawsuit with a lawyer saying anything that comes into his head, he may as well be writing fiction stories. >> reporter: adam's attorney agrees, saying greer's claims are "ever evolving, and utterly baseless" and adam had nothing to do with her death. so how does greer hope to convince a jury? he points to those knots binding rebecca's hands and ankles and says he'll be able to link it to adam's profession. >> the relevance of adam shacknai's profession is he's a tug boat captain. and these were perfect nautical knots. >> reporter: adam admits he handles ropes, but says he doesn't do much knot tying on the river. and his defense expert says there's no such thing as an "exclusively nautical knot." >> the knots are efficient. they're actually probably in the knot-tying world fairly simple. but efficient knots. it shows somebody who understands knots.

>> the evidence unlocking a mysterious death at the sprekles mansion. >> reporter: perhaps the most intriguing piece of evidence is that cryptic message painted on the door of rebecca's room. she saved him. can you save her? greer claims there are similarities between the painted block lettering and adam's handwriting. >> here's the one that i think is really shocking. and that's the "m" on the door, and with that long -- >> this is the m on the door. these are rebecca's ms -- >> rebecca's and all symmetrical up down, up down, except for one. we look at adam over here on other hand, what is on every one of his ms, the last leg is a lengthy long. >> reporter: the san diego sherriff's department never conducted analysis of the handwriting. >> i'm confident with the results of our investigation. >> reporter: they say the block lettering painted on a door can't be compared with handwriting on a page. an opinion shared by both adam's expert and ours. >> in your experience before, have you ever connected the painting like this to naturally

written words or letters? >> not with any degree of certainty. no. >> reporter: years ago, authorities cleared adam of any involvement in rebecca's death. and dina, the woman the zahau family once accused in this civil suit, says she's on his side. >> i don't believe adam shaknai is a murderer. no. i don't. >> reporter: greer just needs to convince 9 out of 12 jurors to win his case. you think adam shacknai killed rebecca zahau by a preponderance of the evidence? >> yes. >> that it's more likely than not that he did it. >> more likely than not. and that's all we have to have is one feather of evidence more. and we prevail. >> reporter: next, adam in the hot seat. will he testify? >> right now it's a 50/50 in my

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get moving with nike adidas under armour and track it all with fitbit! the active brands your family wants kohl's cash for you! this weekend - only at kohl's. >> reporter: almost seven years after rebecca zahau's death, a jury is finally hearing the evidence. >> what is the evidence that

adam shacknai did this? >> reporter: it's a civil case, not criminal. but still, there will soon be a verdict. is adam shacknai responsible? >> she was already dead, or dying, because of manual strangulation. >> reporter: the battle lines are clear. >> not one witness will give any testimony that adam shacknai did any of those things! >> reporter: but the outcome far from certain. >> a lot is going to depend on what adam says at civil trial because he can be forced to the stand. >> reporter: there is no telling if that moment will happen. the testimony only began wednesday. so far, keith greer has only presented a few witnesses. >> my sister was murdered. it is pretty obvious she was murdered! >> reporter: for mary zahau, it's a day long overdue. >> this is all about finding the truth. that my sister did not commit suicide. >> reporter: of course, the family is also seeking an unspecified amount of money in damages. they could be awarded millions of dollars.

>> mr. greer hopes the money will come from me. i will never pay mr. greer a dime. >> reporter: the verdict is probably a month away, but no decision will bring little max back to his mother. >> i have never been as happy as i was when i was with max. maxie was my first child, my only, only biological child, and we had such a special connection. i just miss having a life with him. >> reporter: about six miles to the southwest of the courthouse, the california sun still shines on the spreckels mansion. jonah shacknai no longer owns that famous house. >> it's so eerie. it looks completely different now, but just knowing what happened in that house, and those two horrific deaths, it still gives me the chills to this day. >> reporter: same for dina and rebecca zahau's family. and no matter what law enforcement or the courts say, it's almost as if they had written the end of ann rule's book.

>> the tragic deaths of max shacknai and rebecca zahau may never be solved. they have become party of the lore of corondao and of the spreckels mansion and will never be forgotten. perhaps one day the truth will emerge and hearts can begin to heal. >> and we will continue to follow this case here. the question for you at home tonight, do you think she was killed or was it a suicide? let us know on facebook and on twitter. i'm david muir. for elizabeth and all of us here at "20/20," thanks for watching. have a good evening, and a great weekend. good night. ight. e. a handful of snowboarders versus tons of snow. the desperate dig to free a man

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