this is "nightline." >> tonight, they appeared to be the perfect couple. bob and gale. except bob, the successful doctor, had a dark side. >> the bernbaum story when you get down to it, is dr. jekyll and mr. hyde. >> there were plenty of warning signs. >> bob tried to kill the cat. he had the cat in the toilet, choking it with its head submerged underwater. >> then gale disappeared. without a trace. >> bob calls me. he says is gale still with you? >> no body to bury, no proof of a murder. >> feels completely safe. completely confident that he's gotten away with murder. >> but would he? the special edition of

"nightline," "do no harm," will be right back. did you know that even after you sanitize a surface, every touch can leave new bacteria behind? that means, you could be right back where you started. break the cycle with microban 24. just spray once and your surfaces are protected against bacteria all day. microban keeps killing 99.9% of bacteria touch after touch for up to 24 hours*. these leading disinfectants do not. use the sanitizer 4 out of 5 doctors would use in their own homes microban 24.

i am totally blind. and non-24 can make me show up too early... or too late. or make me feel like i'm not really "there." talk to your doctor, and call 844-234-2424. tall, dark and handsome. this perfect renaissance man. >> the bierenbaum story when you get right down to it it is dr. jekyll and mr. hyde. >> tell me about your sister. what was she like? >> gail was a very gentle soul.

>> gail beth katz was born on march 8th, 1956. the oldest of three children. her family lived in brooklyn, new york before settling on long island. >> i was one year behind gail in school. we were best friends. she was beautiful, smart, and unfortunately anxious. a little bit of depression early in life. she never thought she was good enough. she never knew how good she was. >> reporter: gail hits a low point in 1979 and attempts suicide. >> in my heart of hearts i believe it was more of a really, really big cry for help than a true suicide attempt. >> reporter: over time alayne says gail appeared to bounce back, landing a job at an ad company and building her way back up. >> and that's when one of her friends decides that she's got to introduce gail to dr. robert

bierenbaum. >> reporter: robert bierenbaum met gail during his surgical residency in new york. >> he's close to her age, jewish, classical guitar player. he spoke several languages. he was a gourmet cook. an expert skier. he had mastered instructor level piloting. >> reporter: the doctor swept gail off her feet immediately. >> however, in spite of all of his pluses, there were problems with the relationship. and it was obvious early on. >> when we would be together with them as a couple, he would be very controlling of her. >> reporter: but gail had made up her mind. bob was marrying material. and the two get engaged. but then all of a sudden those red flags about gail's seemingly perfect fiance become four-alarm sirens. >> during the summer of '82 i get the hysterical call from my

sister. bob tried to kill the cat. he had the cat in the toilet choking it with its head submerged underwater. >> he was offended because she seemed to love the cat more than she loved bob. >> no, no, no, alayne, we're going to get rid of the cat and then everything's going to be fine because he's going to believe that i love him. i'm like no, not really. you're going to have to get rid of bob. >> reporter: gail and bob marry in 1982, eventually moving into a two-bedroom apartment on manhattan's upper east side. in a building made famous on "the jeffersons" tv sitcom. >> it might have looked like the perfect couple, but the reality was they were fighting a lot. >> bob had rules. and you'd better follow those rules. >> reporter: the following year alayne says bob violently

attacked gail after he saw her smoking on their apartment balcony, strangling her until she passed out. she reported the incident to the police. >> if this had happened in 2021, robert bierenbaum would have been in handcuffs immediately. the fact that this was 1983, nothing was done about it. >> reporter: gail demands that bob see a therapist. he goes to dr. michael stone, who is so alarmed by bob that he writes a letter. >> the letter went as far as being a hold harmless letter. he didn't want to be held liable for not warning her about the danger. >> the letter says if i do not heed this advice i must accept the consequences including the possibility of personal injury or death at the hands of my husband and absolve dr. stone of responsibility for any such eventuality. >> reporter: were you aware of the letter? >> it says he's a psychopath and he's going to kill me.

>> reporter: why in the world would she stay with this guy after she received that kind of warning? >> i think she didn't believe it. she said to me that i want to get divorced. you know, he really has to do right by me. and if he doesn't i am going to publicize this letter and it's going to ruin him. >> reporter: two years later, on july 7th, 1985, gail goes missing. bob says they had an argument, she left in a huff, and he went to new jersey to attend his nephew's birthday party. >> bob calls me, says is gail still with you? i said what do you mean is gail still with me? i left her yesterday, 5:00. my heart went into my throat. >> she's not with me and she's not with my parents. and at that moment i thought i t

sister's dead. and if she's not alive there is only one person who is a likely suspect to murder her, and it's bob. there's no other suspect. >> on monday july 8th, 1985 about 9:00 in the evening robert bierenbaum came into the precinct to report his wife, gail, missing. >> reporter: bob tells police that they had an argument, then she came here to the park? >> yes. and by the very following weekend we had missing posters made of gail. >> it was almost like pulling teeth to get robert bierenbaum to help. >> reporter: authorities continued to search tore gail and ultimately determined she did not die by suicide in the park. ♪ weeks after his wife's disappearance bierenbaum is seen partying in the hamptons. he's even started dating.

>> even his dress changed from ll bean to saturday night fever. this wasn't the concerned husband. >> reporter: gail's family gets their hopes up about holding bob accountable when investigators make a shocking discovery at a new jersey air field. >> robert bierenbaum, the day his wife disappeared, drove to cole airport sometime in the afternoon. flew a plane for over an hour and a half. returned to the airport and then went to his sister's house for the party. the working theory was that he folded her up, put her in a duffel bag, came out to where we are today, rented his plane, loaded her in the plane, flew out over the ocean and dumped her in the ocean. >> reporter: but the manhattan district attorney tells gail's family it's not enough to bring

charges against bob. >> it was a death sentence for my parents. >> reporter: then in may of 1989, three years after the investigation went cold, a torso washes up on staten island. an x-ray technician compares it with old scans of gail's and says it's a match. >> now we had a body to bury. we have some closure. >> reporter: alayne remains adamant in her pursuit of justice for her sister. >> i would leave messages on his answering machine, you know, telling the woman he was living with he's dangerous, you know, be careful. >> reporter: alayne's relentless efforts appear to pay off. in 1989 robert bierenbaum pulls up stakes and leaves new york city behind. coming up -- >> feels confident that he's gotten away with murder. >> robert bierenbaum had

absolutely no idea it was coming. for people living with h-i-v, keep being you. and ask your doctor about biktarvy. biktarvy is a complete, one-pill, once-a-day treatment used for h-i-v in certain adults. it's not a cure, but with one small pill, biktarvy fights h-i-v to help you get to and stay undetectable. that's when the amount of virus is so low it cannot be measured by a lab test. research shows people who take h-i-v treatment every day and get to and stay undetectable can no longer transmit h-i-v through sex. serious side effects can occur, including kidney problems and kidney failure. rare, life-threatening side effects include a buildup of lactic acid and liver problems. do not take biktarvy if you take dofetilide or rifampin. tell your doctor about all the medicines and supplements you take, if you are pregnant or breastfeeding, or if you have kidney or liver problems, including hepatitis. if you have hepatitis b, do not stop taking biktarvy without talking to your doctor. common side effects were diarrhea, nausea, and headache. if you're living with hiv, keep loving who you are.

and ask your doctor if biktarvy is right for you. when you're driving a lincoln, if you're living with hiv, keep loving who you are. stress seems to evaporate into thin air. which leaves us to wonder, where does it go? does it get tangled up in knots? or fall victim to gravity? or maybe it winds up somewhere over the bermuda triangle. perhaps you'll come up with your own theory of where the stress goes. behind the wheel of a lincoln is a mighty fine place to start. (upbeat pop music throughout) (upbeat pop music throughout)

♪ dr. robert bierenbaum leaves new york city in 1989. the district attorney has closed its investigation into gail's death without bringing any charges. he starts a new life in las vegas as a hotshot plastic surgeon. even joins i charity providing

free medical care to disadvantaged children. >> he kept his secrets to himself. >> reporter: he gets a girlfriend, stephanie youngblood. >> the first year was perfect. fun, fun, fun. we went on a lot of ski trips. >> reporter: stephanie notices a tag on his luggage that says "gail bierenbaum" and asks who that is. >> he got kind of emotional. and he told me he had been married before and they had a big fight and she took off for central park and she disappea disappeared. >> reporter: stephanie says bierenbaum told her he had been thoroughly investigated by the cops and cleared of all wrongdoing. >> the way he told the story it was believable. >> bob's image on paper was real. but cracks started to appear. >> reporter: one time he erupts after she asked for a glass of wine and the bottle sprayed

everywhere. >> my life was flashing in front of my eyes. >> reporter: alarmed by that incident, stephanie says she demanded they see a therapist. >> we only had one session, and she goes, there are issues there, that my life could be in danger with him. and so i started to build a strategy to leave. >> reporter: stephanie does leave and bob quickly moves on. marrying a gynecologist in june of 1996. he moves with his new wife, janet, to minot, north dakota where they both work at trinity medical center. >> in november of '98 janet and bob had a baby daughter. >> after he left las vegas and moved to north dakota, i'm confident he thought he's never going to have to deal with this ever again. >> while bob was building a new life in the dakotas, back in new york there was somebody who

couldn't forget the disappearance of gail. that guy was andy rosenzweig, the chief investigator of the manhattan district attorney's office. >> reporter: the d.a.'s office has just created a cold case unit. rosen zweig assigned steve saracco and dan bibb to the bierenbaum case. >> the first thing that stood out to me when i reviewed the file were the flight records. there's the explanation why gail is not around anymore. >> that coupled with his visits to his psychiatrist dr. michael stone. i called stone, cold-called him, and he said of course he killed her, dr. bierenbaum's a dangerous psychopath, this case has been burning on my brain. >> reporter: in the summer of 1998 gail's body was exhumed, but the dna of that torso did not match gail's. >> i am so devastated.

and i looked up at dan and at steve and i said, "now you better get a conviction." >> in late november of '98 we decided to send investigators to north dakota to see if we could get some kind of statement. >> he's feeling as safe as you possibly can. all of a sudden now he sees these guys from manhattan telling him we're here because we're investigating -- reinvestigating your wife's disappearance. >> reporter: then in september of 1999, 14 years after gail's disappearance, a grand jury indicts robert bierenbaum for second-degree murder. robert bierenbaum will be returning to new york city, this time to stand trial for gail's murder. >> it was an unusual case with a

lot of difficult legal issues, and one of them would be of course that there was no body because then you wonder how the prosecution is going to prove that there was in fact a murder. >> it was a key thing for the prosecution to let the jury see how bierenbaum had abused his wife during their marriage, including the 1983 choking incident. >> reporter: gail's sister and friend testify about that ominous letter from dr. stone. another critical part of the prosecution's case, the discovery that bierenbaum had flown his plane on the afternoon of july 7th, the day gail went missing. prosecutors are able to show jurors bierenbaum's own personal flight log, where the 7 for july had been apparently altered to an 8. >> a big hurdle for the prosecution was to persuade the jury that someone could actually fly a plane and push a body out the door and not crash.

>> the sergeant showed that not only was it possible to dispose of the 110-pound bag, that it actually was very easy, he could do it either from the pilot's door, which he did, or from the passenger door. >> reporter: over the course of the trial the prosecution calls 34 witnesses. >> the defense did go into other reasons why she could have gone missing. they brought up mental health issues, the possible drug use or infidelities. >> ultimately, i think what they did led nowhere. >> reporter: 15 years after gail's disappearance the case finally goes to a jury. after just 5 1/2 hours of deliberation there's a verdict. >> the foreperson stands up and says guilty. and there was a buzz in the

courtroom. >> we trembled and we cried. >> there are very few cases in which someone has been a law-abiding citizen and has done good things. so i gave him 20 years to life. >> he spent the first 10 years behind bars trying to prove his innocence and get his verdict overturned. he appealed in state courts, federal courts, got nowhere. just last december, after 20 years behind bars, the parole board denied him freedom. >> reporter: there was no public reason given for the decision, but "20/20" obtained this transcript of that parole hearing, and in it is a shocking revelation. to the parole board bierenbaum said, "i wanted her to stop yelling at me, and i attacked her." when he's asked "how did you attack her," he responds "i strangled her."

bierenbaum goes on to say, "i went flying. i opened the door and then took her body out of the airplane over the ocean." >> i was stunned when i heard he admitted it. >> i was in shock. and i cried. >> reporter: he said he killed gail because he was immature and didn't understand how to deal with his anger. the parole board noted that at the time he was a 29-year-old medical doctor. >> this is what happens so often in domestic violence cases. the victim could have been saved. >> reporter: gail's family established gail's house at the pace women's justice center to support domestic violence victims. >> my sister's body has never been found. gail's house gave my sister a

resting place. i feel my sister's spirit is here. it is warning others, inspiring others. cabenuva is the only once-a-month, complete hiv treatment for adults who are undetectable. cabenuva helps keep me undetectable. it's two injections, given by a healthcare provider once a month. hiv pills aren't on my mind. i love being able to pick up and go. don't receive cabenuva if you're allergic to its ingredients or taking certain medicines, which may interact with cabenuva. serious side effects include allergic reactions post-injection reactions, liver problems,...and depression. if you have a rash and other allergic reaction symptoms, stop cabenuva and get medical help right away. tell your doctor if you have liver problems or mental health concerns, and if you are pregnant, breastfeeding, or considering pregnancy. some of the most common side effects include injection site reactions, fever, and tiredness. if you switch to cabenuva,

attend all treatment appointments. with once-a-month cabenuva, i'm good to go. ask your doctor about once-monthly cabenuva. don't settle for products that give you a sort-of white smile. try crest whitening emulsions... with once-a-month cabenuva, i'm good to go. ...for 100% whiter teeth. its highly active peroxide droplets... ...swipe on in seconds. better. faster. 100% whiter teeth. shop crestwhitesmile.com. align. fast acting biotic gummies helps soothes occasional abdominal discomfort, gas, and bloating and it works fast. in as little as 7 days try fast acting biotic gummies from align. the #1 doctor recommended probiotic brand. the classic hollywood story. we meet the hero, the all-new nissan frontier. hero faces seemingly impossible challenge. ♪

tension builds... ♪ the plot twist. ♪ the hero prevails. in hollywood, this would be the end. but our here, we are just getting started. introducing the all-new nissan frontier. every day in business brings something new. but our here, we are just getting started. so get the flexibility of the new mobile service designed for your small business. introducing comcast business mobile. you get the most reliable network

with nationwide 5g included. and you can get unlimited data for just $30 per line per month when you get four lines or mix and match data options. available now for comcast business internet customers with no line-activation fees or term contract required. see if you can save by switching today. comcast business. powering possibilities. i am totally blind. and non-24 can throw my days and nights out of sync, keeping me from the things i love to do. talk to your doctor, and call 844-214-2424.

our thanks to john. you can see more of "20/20's" "do no harm" and all of our episodes on hulu. and finally tonight, if you or someone you know might be struggling, the national domestic violence hotline is always open. dial 1-800-799-7233 confidential assistance. we'll see you right back here same time monday. thanks for staying up with us. good night, america.