>> hello, i'm adrian canning. and this is dateline. >> she was a wife, she was a mother. >> she was the most amazing woman i had ever met in my

life. and then, suddenly, one day, she was gone. poisoned by carbon monoxide. >> he's like, i couldn't get a pulse! i couldn't get a pulse! i couldn't get a pulse! >> her husband blamed of faulty water heater. police blamed him. >> you don't think this is an accident. >> no. >> there was just one problem. and it was a big one. no one could figure out exactly how he might have done it. >> he's an expert at gases. >> murder or accident? >> did you kill your wife? ♪ ♪ ♪ >> hello and welcome to dateline. hundreds of americans die every year from accidental carbon monoxide poisoning. according to police in ohio, one of those deaths wasn't an accident. it was murder. they say if anyone would know how to use a deadly gas to

murder someone, it was their prime suspect. here is kate snow with deadly exposure. >> he has come back to where it all began, to the tune, the streets he knew so well, remembering the old times when life was simple, love was young and the future held so much promise. taking time to reflect on how it happened. a few days from now, it will all be over, one way or another. >> my carbon oxide detector is going off and my wife is having a seizure. >> our story begins in ohio, on a frantic, -- september 4th, 2006. dr. mark wangler says he woke suddenly in the dancers master bedroom to the sound of an alarm. >> just a loud, piercing noise.

able to determine it was the carbon monoxide detector. i ran to check on kathy. >> kathleen wangler was 43 years old. for most of her life, had suffered from epilepsy. she was sleeping upstairs. >> i went in and shook her, called out to her, screamed at her. she wasn't responsive. i called 9-1-1. >> you tell them that she is having a seizure. >> yeah. >> is she breathing? >> no, i think she's not breathing. >> okay, sir, i need you to check for me. >> no, she's not breathing. >> okay, does she have a heartbeat? >> no, she doesn't. >> do you remember doing cpr? >> yes, i do remember doing cpr. >> i'm starting cpr. >> okay. >> next door neighbor, diane, saw the rescue squad at the wangler's home. >> i went over and i said, mark, did kathy have a seizure? he's like, i couldn't get a pulse, i couldn't get a pulse,

i couldn't get a pulse! >> the emts took kathy to the memorial hospital. mark followed along and diane was close behind. the news came in a matter of minutes. kathy was dead of acute carbon monoxide poisoning. >> do you remember when they told you she had passed? >> no, i do not. >> why do you think you don't remember any of that? >> i was poisoned with carbon monoxide. >> it's an odorless, tasteless, colorless gas. as a doctor, mark wangler says he knew he had been put poisoned with carbon monoxide because his head hurt and he felt so disoriented. neighbor diana says she remembers how mark took the news of kathy's death. >> he sought like a baby. tears were rolling down his cheeks. he was like, you know, this. he couldn't believe it had happened. >> i wanted to see kathy's face. i want to see kathy. >> to say goodbye?

>> yeah, it was tough. >> kathy's family members drove to live up memorial. they'd only been told there had been some kind of accident. they found their way to a waiting room. >> they told us in the room, it was a hard moment. it's hard to see your parents cry. and that, turn around you call your brothers and sisters. >> mark wangler called his two sons, nathan and erin, who were living in cincinnati. aaron was in his second year of college. >> i just remember screaming and crying. it was horrible. >> the brothers rushed home to their father in lima. >> my brother and i held each other, sobbing and crying. his body was shaking from crying so hard. >> thousands of people are accidentally poisoned with carbon monoxide every year. it usually happens in something

like a space heater or a furnace or a water heater malfunctions. it has to gators wanted to find out quickly, what went wrong at the wangler home? a detective came to speak with mark wangler here at the hospital. >> former allen county sheriff, sam creche, read the detective bureau back then. he says wangler mentioned that water heater. >> dr. wangler made a comment, we've been having problems with this water heater for the past few weeks. the flame would go out occasionally. i felt that that was the problem due to the carbon monoxide detectors going on. >> diane remembers her husband was worried about the wangler's water heater, saying the exhaust pipe on the roof was in place there correctly. could that have caused a backup of carbon monoxide in the house? >> he told mark, that would scare me to death, mark. >> it sounded like mark wangler was lucky to be alive. kathy just happened to be the ones sleeping upstairs that night. mark was downstairs.

it seemed like a sad, but explainable accident. as it turns out, it wasn't so simple. >> coming up -- growing suspicions that something was missing. >> we walked around the house with the water heater, looked at the other appliances. we couldn't find a source. >> for the carbon monoxide? >> right. the appliances appear to be working properly. >> when dateline continues. nues trelegy for copd. ♪ birds flyin' high, you know how i feel. ♪ ♪ breeze driftin' on... ♪ [coughing] ♪ ...by, you know how i feel. ♪ if you're tired of staring down your copd,... ♪ it's a new dawn, ♪ ♪ it's a new day... ♪ ...stop settling. ♪ ...and i'm feelin' good. ♪ start a new day with trelegy. no once-daily copd medicine has the power to treat copd in as many ways as trelegy. with three medicines in one inhaler, trelegy makes breathing easier for a full 24 hours, improves lung function, and helps prevent future flare-ups.

trelegy won't replace a rescue inhaler for sudden breathing problems. tell your doctor if you have a heart condition or high blood pressure before taking it. do not take trelegy more than prescribed. trelegy may increase your risk of thrush, pneumonia, and osteoporosis. call your doctor if worsened breathing, chest pain, mouth or tongue swelling, problems urinating, vision changes, or eye pain occur. take a stand, and start a new day with trelegy. ask your doctor about once-daily trelegy, and save at trelegy.com i'm a bear. i'm coming out of hibernation after the best nap of my life... and papa is hungry. and while you're hittin' the trail, i'm hitting your cooler. oh, cheddar! i've got hot dog buns! and your cut-rate car insurance might not pay for all this. so get allstate, and be better protected from mayhem, like me. roar. (sfx: family screams in background)

and this is ready to go online. roar. any questions? -yeah, i got one. how about the best network imaginable? let's invent that. that's what we do here. quick survey. who wants the internet to work, pretty much everywhere. and it needs to smooth, like super, super, super, super smooth. hey, should you be drinking that? -it's decaf. because we're busy women. we don't have time for lag or buffering. who doesn't want internet that helps a.i. do your homework even faster. come again. -sorry, what was that? introducing the next generation 10g network only from xfinity. >> welcome back to dateline. the future starts now.

kathy wangler was found dead in her home. the cause? carbon monoxide poisoning. it seemed like an open and shut case. accidental death. kathy's husband, mark, told police they had a penalty water heater, but police weren't convinced he was telling all he knew. once again, here is kate snow with, deadly exposure. >> 48-year-old kathy wangler had a personality that filled the room. now, she was gone, killed by carbon monoxide. for her family and friends, it was a terrible loss. her sons, nathan and aaron, it was devastating. as he told, us they adored their mother. >> she was amazing. the most amazing woman i have ever met in my life. did everything for everyone.

always put my brother and i as the number one priority in her life and our dad. >> she certainly didn't want to be defined by her epilepsy. it started when she was a little girl, but medication seem to keep it under control for the most part. kathy was 15 when she met mark wangler. >> grip in a little town of recovery, ohio. in the middle of the state. near the ohio indiana border. about 1200 people. >> what was that like? >> i enjoyed it. i really looked growing up in a small town. we put softball in that backyard and you knew your neighbors, you know everyone in town, everyone in town knew you. my dad owned a hardware store. >> that's where mark met kathy's grandfather, a customer at the store. one day when mark stopped by the grandfather's house for a visit, he met kathy. kathy's mother remembers a couple of months later, mark was back. >> the kids committing go, mark is here! mark who? and they said, mark wangler.

i said, where is he? he was out, he brought his guitar and came in set on the back of the truck, of his vehicle. and was strumming guitar, singing to kathy. >> serenading her? >> yes. yeah. >> they started dating. a few years later, 1977, mark and kathy got married. he was 21, she was 18. they had their wedding in a catholic church. by that, mark had embraced an evangelical christian faith. >> they were the happiest to people i've ever seen. >> it turns out the quiet young man from fort worth, recovery, had big ambitions. he wanted to be a doctor. kathy worked to put mark through med school. things were tight. >> were you happy in those years? >> yeah. >> you had two boys. >> correct. >> nathan and aaron were born right as mark was beginning his practice. >> we get hugs and kisses every

morning and every night before you go to bed, when you look for school or even if you are going out to hang with your friends, forever. we always kiss and we were very close family. >> they moved to lima in 1990. by that, the christian faith had become very important to mark wangler. they join grace baptist church. >> what was it about this particular church that you and coffee both thought was a right fit? >> two things. one of them is if all the people there for friendly and the pastor was correctly preaching god's word and the second thing is that they had a children's program, a youth program. >> mark and kathy and the boys. >> at the time, mark's medical practice was growing. >> merry christmas! >> after those early years of doing without, the family was now well off. they took the boys on vacations, camping, europe. kathy went back to school, did some substitute teaching. life seemed to be going well

for the wangler's. next door neighbor, diane, was fond of both caffey and mark. >> mark was more reserved. nice man, very patient and caring person. would help you out and do anything for you. you know, he had his peculiar ways about him. a little dorky and he looked different from other people until you get to know mark and he is the most wonderful person you could ever meet. kathy was a lot of fun to be around. she was lovely, had a crazy laugh. loved life. just a lot of fun. >> now, after 29 years of marriage, two boys, a prosperous life, kathy wangler's life had ended in one terrible morning. how did it happen? mark wangler had told investigators he thought it was probably the water heater. so, they check that out.

the allen county prosecutor was concerned by what they didn't discover. >> prosecutor jurgen often examines the seeds of unexplained deaths and allen county. >> we walk around to look at the water heater, look at the other appliances, asked for the gas logs, the garage, also the bedroom where kathy wangler died. >> they couldn't find a problem with any of the appliances. >> we just couldn't find a source. >> the carbon monoxide? >> right. because the appliances, at that point, appeared to be working properly. >> investigators now had a mystery on their hands. they returned to the wangler house to do some rechecking. and then, in december 2006, three months after kathy's death, mark wangler says investigators told him they had looked at everything. they still didn't know what had happened, they said. they were satisfied it was an accident. >> they were settled? >> that was what i was told. >> mark was slowly trying to

build a new life. some members of kathy's family weren't ready to move on. they were still asking questions. they thought the answers just might lie with mark wangler. >> coming up -- >> i said, we have so many questions and nothing is being answered. >> what did kathy's family know that made them so suspicious? >> she got in the car. the boys got in the car. mark was hanging on the side of the car. kathy was driving away, yelling at him. >> when dateline continues. ♪♪ allergies don't have to be scary. (screaming) defeat allergy headaches fast with new flonase headache and allergy relief!

two pills relieve allergy headache pain? and the congestion that causes it! flonase headache and allergy relief. psst! psst! all good! protect your dog from heartworm disease every month with heartgard plus chews. digestive and neurologic side effects have been reported. for a limited time, get up to a 2-month rebate when you buy 12 doses of both heartgard plus chews and nexgard chews from your vet. terms apply. (rebecca) it wasn't until after they had done the surgery to remove all the toes that it really hit me. you see the commercials. you never put yourself in that person's shoes until you're there. (announcer) you can quit. call 1-800-quit-now for help getting free medication. (vo) this is sadie, she's on verizon. the network she can count on. call 1-800-quit-now for and now she's got myplan, the game-changing new plan that lets her pick exactly what she wants and save on every perk. sadie is getting her plan ready for a big trip. travel pass, on. nice iphone. cute couple. trips don't last forever, neither does summer love. so, sadie is moving on. apple music, check! introducing myplan. the first and only unlimited plan to give you exactly what you want,

so you only pay for what you need. act now and get iphone 14 pro max on us when you switch. it's your verizon. ♪ upbeat music ♪ ♪ [ tires screeching ] director: cut! jordana, easy on the gas. force of habit. i gotta wrap this commercial, i think i'm late on my payment. it's okay, the general gives you a break when you need it. yeah, we let you pick your own due date so you can pay your car insurance when it's best for you. well that's good to know, because this next scene might take a while. [ helicopter and wind noises ] for a great low rate, go with the general.

♪ this is not just delivery. ♪ this is knowing even superheroes... can use a sidekick. ♪ walgreens. >> kathy wangler's death

certificate says the cause was carbon monoxide poisoning, but what was the source? by december 2006, three months after kathy's death, that question had grown more urgent in the minds of her family members and sister, diana, wanted answers. >> it was kind of like the white elephant in the room. none of us wanted to talk about it. the police weren't calling us. i felt as if nothing was getting done. >> so, diana decided she had had enough. >> i called mom and she called the sheriff's department. >> i said, we have so many questions and nothing is being answered. >> but it wasn't just questions

kathy's family had. they also had suspicions about mark. they knew something. the wangler marriage was a disaster and they wanted police to know the problems went back years. >> kathy had told me mark had an affair. >> that kind of been easy for her sister. >> she could never forgive him for that. >> they managed to carry on. over the years, kathy's family remembers simmering tensions that could erupt into open warfare. they say mark thought kathy gained too much weight. she wouldn't clean the house. she spent huge amounts of money. kathy got mad at mark a lot. diana recalls what happened right after they took this family portrait. mark and kathy were fighting again. >> she got in the car, the points got in the car. mark was hanging on the side of the car. kathy was driving away, yelling at him. at one point, one of the boys jumped out and there was a lot of yelling and carrying on.

and then kathy left with the boys. >> mark wangler admits things did go downhill after the boys left for college. he says kathy would get deeply depressed. >> but the boys being gone, she lost her purpose in life, i would say. >> we're working on it? were you trying -- >> yeah, we were in counseling. >> that, she was gone. kathy's family knew she had been sleeping upstairs while he was downstairs, but then they heard what mark had told investigators and a collective alarm went off. mark said he was sleeping with a towel under the bedroom door, a fan blowing and the bathroom window open. it was because the toilet and the master bath through head overflowed and mark said he wanted to keep the smell out of the rest of the house. kathy's family knew about the problem with the toilet, but they figured there was a different explanation for the towel, the fan and the open window. they believed mark knew there was carbon monoxide in the house because he had somehow

put it there and he was protecting himself from poisoning. >> how did you respond to that suspicion that was placed on you? >> i was devastated. >> five miles of dirt kathy died, her case file landed on the desk of a veteran detective, clyde, since retired. >> what is your instinct? >> in reading reports, i was sure that the water heater, the furnace and the fireplace were not the source of a carbon monoxide. so then you have to think, okay, what else in that house can produce carbon monoxide? there is a generator in the garage, two cars in the garage, a snow blower in the garage. those all produce carbon monoxide. >> of course, all of those things need someone to turn them on. >> you don't think this is an accident? >> no. >> still, if it wasn't an accident, how could someone pull that off, fill an upstairs bedroom with enough carbon monoxide to kill? detective knew it sounded

improbable, but he kept thinking about the logic of that other detective, sherlock homes. >> it was a matter of eliminating the impossible things and at the end, you're stuck with the improbable. >> there is another clue that the taj active and the county prosecutor couldn't ignore, dr. mark wangler had a specialty. >> he's an expert in gases. is it analyses yellow. just >> that's right, and at a cz-ologist. a doctor that knows exactly how to put people to sleep. did he use his expertise to kill his wife? in april 2007, seven months after kathy's death, detective got a search warrant for the wangler home. he had a videotape running as officers sees the computer, papers, and mark's journals. detective says the journals really caught his attention. >> you have to read the whole thing. i cannot explain, i wish i could.

he was at the end of his rope. i think he felt trapped. >> now, all of these months later, mark wangler's life was on the upswing. he had reconnected with an old friend who shared his faith, esther, a romance blossomed. >> you ended up getting married a year after kathy's death. >> 14 months, correct. >> some people might think that's pretty fast to bounce back. >> we heard that. >> and the wedding bells had barely stopped ringing when detective got a second search warrant. by now, he had come to believe that mark wangler was a killer. the detective thought that would have used an engine of some sort, a portable generator or maybe the vehicles, to put carbon monoxide into the heating system of his home to kill his wife. the detective wanted someone to take a closer look inside the heating ducts of the wangler home. >> we went in and dismantled

the ductwork and took carpet samples and registers out of the house. >> investigators found the lab to determine its soot from internal combustion engine could be found inside the heating ducts. it would be months before they got results. >> do you have any idea that as having this busy, happy time, the investigation was still trying to put a case together? >> we really didn't hear anything. >> we didn't hear anything at all, no. >> you planned a trip to zambia. why did you end up there? >> one of the churches in town, a good friend of mine, had gone to zambia with several people from his church. >> they learned that people in zambia were in dire need of freshwater. so, mark and esther joined a church mission to help dig wells there. >> after three weeks, it was time to go home. >> you land in atlanta and your son calls. >> he said, you know some guy

named -- he was being on the door. >> the detective? >> yeah. >> you knew then? >> so, we know that. and the atlanta airport that there must have been an indictment. they were at the door to arrest mark. >> the lab results were in on that ductwork. >> coming up -- prosecution's case? a motive? >> we have some diaries that are pretty dark and lay out the state of marriage was. >> and leads. >> can you tell the jury what, if anything, was in that particular bedroom? >> i observe something like marks in the walls directly about the heat register in their. >> when dateline continues. continues - i'm fernando, i live outside of boston.

i've been with consumer cellular for five years. consumer cellular gives you all the same features that these big companies give you. what you get for the cost is remarkable. why would you pay more money?! - [announcer] why would you pay more when you can get unlimited talk & text with a flexible data plan starting at just $20 a month. - i think they should raise their prices! (laughs) - [announcer] sorry fernando! our prices are staying low. so switch today and save! call or go online. my mental health was much better, but i struggled with uncontrollable movements called td, tardive dyskinesia. td can be caused by some mental health meds. and it's unlikely to improve without treatment. i felt like my movements were in the spotlight. ingrezza is a prescription medicine to treat adults with td movements.

ingrezza is different. it's the simple, once-daily treatment proven to reduce td that's #1 prescribed. people taking ingrezza can stay on their current dose of most mental health meds. ingrezza 80 mg is proven to reduce td movements in 7 out of 10 people. don't take ingrezza if you're allergic to any of its ingredients. ingrezza may cause serious side effects, including sleepiness. don't drive, operate heavy machinery, or do other dangerous activities until you know how ingrezza affects you. other serious side effects include potential heart rhythm problems and abnormal movements. it's nice people focus more on me. ask your doctor about #1 prescribed, once-daily ingrezza. learn how you could pay as little as zero dollars at ingrezza.com ♪ ingrezza ♪ >> i'm katie phang.

here's what's happening. the man who killed at the tree of life synagogue a in 2018 was found guilty of federal hate

crimes. the jury will now decide if the defendant, robert bowers, should get the death penalty. meanwhile, president biden spoke at the safer community segment and connecticut to mark the one year bipartisan bill to stop people from accessing guns. he said more still needs to be done for the sake of children who are now suffering the same trauma as soldiers. now, back to dateline. now, back to dateline. >> welcome back. i'm a jury can. kathy wangler died of carbon as a poison in her home. a couple years later, investigators thought that they had enough to -- her husband of 29 years. here again is kate snow with deadly exposure. >> on september 19th of 2009, as mark wangler boarded a plane

from atlanta to ohio, he knew he was about to be charged with killing his first wife of three years earlier. >> i felt i needed to come back and clear my name. >> two days later, sheriff's deputies came to the couple's home and arrested mark wangler. he was charged with aggravated murder. the trial took place in march 2011 but the allen county courthouse. prosecutor, juergen, didn't have fingerprints, dna or an eyewitness. he believed the evidence would show that dr. mark wangler killed his wife while she was sleeping using engine exhaust using deadly carbon monoxide. >> carbon oxide poisoning, really high-level, 69%. i have a defendant who has low levels. we have no legitimate source of carbon monoxide in the home. and we have some diaries that are pretty dark and lay out what the state of the marriage was. >> and that is where prosecutors started, with the

marriage, the motive. kathy's family bolstered the argument that the marriage was a miserable one. >> he criticized her weight. he didn't like her hair. >> did you ever hear marc criticize kathy on the topic of money? >> yes, he didn't like her shopping. >> prosecutor suggested marc become increasingly angry about his wife spending. just after kathy died, mark showed investigators this cash, jewelry and credit cards he found kathy's car. so, why not to force? friends and family testified kathy wouldn't leave the marriage because she was afraid mark would cut off her money. as mark -- >> the defendant was deeply obsessed with religion and a divorce would cause him to lose his standing and reputation in the church. >> if mark and kathy were stuck with each other and fighting all of the time, his journals painted an even bleaker picture. the man who wrote them wasn't just unhappy, he was depressed. according to prosecutors,

desperate enough to kill. >> detective took the jury through each painful entry. >> i'm tired of her lies and heidi huge amount of money from me. she turns away each time i kiss her. she continues to reject my love towards her. i truly long to serve jesus, but i became weak from the wounds satan throws at method from within my own family. >> just two months before kathy wangler died, mark wrote this. >> thoughts of suicide are strong again. satan is attacking me in a new way this time, using car exhaust. >> that's a red flag. tells you the state of someone's marriage in our assessment that if your marriage is so bad they want to kill yourself, what other things are you willing to do? >> and that mention of car exhaust really got their attention. one depressing entry after another, mounting evidence of a man in misery. and as prosecutors, a motive.

>> 9-1-1 -- >> and that 9-1-1 call raised even more suspicion as far as the prosecution was concerned. >> hello? >> i'm still here, sir. >> okay, i'm trying to breathe for her. >> okay, 1000th. >> okay, thanks. >> i'm starting cpr. >> okay. >> it just didn't sound like he was doing cpr on the 9-1-1 call. it's not like the whole thing was staged. >> and if dr. mark wangler was doing cpr, why with the fire chief find kathy on an air mattress? >> for adequate compressions, it should be on a hard surface, yes. >> is that pretty basic cpr stuff? >> yes. that is basic cpr. >> something even more important crossed the chief's mind after he found kathy. this was a huge red flag for prosecutors. he said cathy's body was cool to the touch. odd since mark told 9-1-1 that her heart stopped beating only minutes before. >> we discussed with each other, in the ambulance on the way to

the hospital, that she was cold. >> which would've been unusual for someone who was just minutes before breathing in a heartbeat? >> that's correct. >> the e.r. doctor backed him up on that. >> she had rachael temperature that was quite low. my documentation said it was like 94. >> the doctor also testified the body seem to be getting stiff. >> it seemed like she had been dead for a while. >> in other words, dead before her husband called 9-1-1. there was more. the prosecution suggested mark wangler's grief was phony. >> what was his emotional state that you observed at that point? >> he was acting like he was crying, but i didn't really see normal stuff when you cry. you know? >> and the days that followed kathy's death, investigators tested and retested the water heater and other appliances. prosecutors reminded the jury that there was no sign any appliance had accidentally released carbon monoxide.

and that was the crux of the case. >> it either had to be the water heater or it was murder. that's the bottom line. >> and if it was murder, how would he have done it? prosecutors believe mark wangler closed all of the heating fence except the ones in kathy's room. then, he must have shut the doors to the furnace room, except the one leading to the garage. he could have started a car or a generator, maybe both, and filled the garage with carbon monoxide. a carbon monoxide with and find the only open path, down the stairs, into the fairness. the deadly gas would then travel through the heating ducts and out the vents in kathy's room. they pointed to pictures taken to kathy's room after she died. >> can you tell the jury what, if anything, you notice in that particular bedroom? >> i observed a soot-like marking on the wall, directly above the register, the heat register in their. >> nobody actually tested that stain on the wall before it was

painted over her. prosecutors were prepared to show that engine exhaust had come through the heating ducts and out of those beds. prosecutors now presented the key scientific evidence designed to wipe out any remaining doubt about the source of the carbon monoxide. lab chemists had tested the inside of the heating ducts and said they indeed found soot that shouldn't have been there. >> can you say to reasonable degree of scientific certainty that exhaust from a combustion source flows directly introduced into the ventilation system? >> he has. >> can you say first scientific certainty that the water heater was not the source of the soot in the ventilation system? >> yes. >> devastating for mark wangler's case, maybe. maybe not. >> then a faulty water heater cause kathy wangler's death? was the prosecution's case all just hot air? >> coming up -- >> it is a gentleman, you will hear from our experts that this

is a junk science as applied to the facts of this case. you will find that there is reasonable doubt, you may even find that the water heater did it. regardless, you will not find that dr. wangler murdered his wife. because he did not. >> when dateline continues.

>> dr. wangler, did you kill your wife kathy? >> absolutely not. >> he had waited more than

three years to defend himself. and all the time, his sons stood by him. and against their mother's family. >> when you have your family setting the back, trying to destroy your family, what you have left, it's hard. it hurts. >> it was time now for the defense to present its case. time for defense attorney, chris mcdowell, to show the jury a different version of the man who stood accused. it is opening argument, mcconnell said that mark was, above all, a devoted christian, who would never commit murder. >> mark did not believe it was good enough just to profess the words of christ or go to church, he felt he had to live it. >> mark wangler's defense came down to this. his wife died in a horrible accident. prosecution never proved the crime was even committed. >> ladies and gentlemen of the jury, dr. mark wangler is innocent. this case has been brought as a

result for poor police investigation, an investigation despite what you just heard from the prosecution, did not eliminate fugitive carbon monoxide as a source from the hot water heater. >> the water heater was now at the heart of the wangler defense. if the jury believed it malfunctioned that night could've sent carbon monoxide in kathy's room, that was reasonable doubt. >> are you worried that a jury won't, in the end, believe your story? >> sure. it's always a possibility. >> do you think about what it would be like? a south to last of your life in prison. >> i try not to. for the most part. >> sounds erin and nathan provided key testimony. >> how would you describe your father? >> i'm great now. very humble, passionate, caring. >> very relaxed, down to earth.

very humble. >> have you ever, for a moment, doubted your dad's innocence? >> never once. >> both erin and nathan said they believe their parents really did love each other. >> up to the day of her death, deeply pure father loved your mother? >> absolutely. >> and then, the defense turned to the mark wangler journals, with their depressing entries about the marriage. the defense challenge the detective. didn't the diaries portrait a man working on his marriage? >> mark praise for a good relationship with his wife, correct? >> yes, he does. >> and he praised that his wife will also see the way you mark on the relationship to, doesn't he? >> yes. >> then, the forensic evidence. prosecutors had said kathy's low body temperature showed mark had killed her with carbon monoxide before he called 9-1-1. >> but the question was, when exactly did that poisonous gas

kill her? prosecution had argued she was already dead when her husband called 9-1-1 because her body was so cold. but how cold was it? apparently the e.r. doctor got the temperature wrong. >> this is the nurses handwritten notes, indicating that the body temperature, rectal temperature, is actually 1.5 degrees more than what you had written and other notes. is that correct? is that yes, ma'am? >> yes. yes. >> okay. >> so, cathy's body wasn't as cold as the doctor thought. considering this, a leading forensic pathologist testified that her heart could've easily stopped exactly when mark wangler said it stopped, during the 9-1-1 call. the defense also had to knock down evidence from the wisconsin lab. the lab expert said they found soot inside the wingless heating ducts that came from engine exhaust. >> this is junk science as applied to the facts of this case. >> mcdowell said other reputable agencies like the fbi

and the ohio state criminal lap refused to do the testing. it was too unreliable. >> these people in wisconsin set, we've never done it before, but we can try it. >> modal attacked the lab's data, the record keeping and its expertise. >> prior to your work involvement in this case, you had no previous experience in conducting analysis on ductwork, did you? >> no, we've not done ductwork before. >> and then, this question. did the lab consider other sources of soot? >> you would agree that candles are potential source of such, correct? >> yes. that is correct. >> candles. the wangler house was full of them. according to testimony from several witnesses like side, aired wangler. maybe that is why the heating ducts were full of soot. >> do you recall if your mother ever burned any [inaudible] >> all of the time. we had tons of candles. >> remember those soot stains coming out of the registers in

the room kathy died? that was aaron's old room. >> those marks were there before i moved for college. that was back in 2004. >> the prosecution's murder scenario involved vehicle exhaust and furnace was preposterous. it had to be the simple explanation, kathy's death was an accident. now came the most important testimony in the defenses case. an environmentally toxicologist testified that most likely source of carbon monoxide was the water heater. >> what was the closest source of carbon monoxide? >> the water heater in the basement of their home. as i recall, pretty directly below her bedroom, two floors up. >> the water heater, he said, was a disaster waiting to happen. one code violation after another. >> my major concern was that this water heater wasn't in the open as most water heaters are. it wasn't a sealed kept it.

>> closed up in that box, he said the unit could have been deprived of oxygen, creating a risk of carbon monoxide. he said venting was another problem. the fedcap was the wrong kind and the exhaust pipe was set too low on the roof. it was all installed so poorly, he suggested, that deadly carbon monoxide could have backed up into the home. the water heater was so faulty, said mcdowell -- >> you will hear from our experts that this is junk science as applied to the facts of this case. you will find that there is reasonable doubt. you may even find the water heater to this. regardless, you will not find that dr. wangler murdered his wife, because he did not. >> coming up -- >> yet expert testimony on both sides of this. >> right. >> did it come down to science for you? >> i don't think so. >> no. >> the verdict. >> the jury find the defendant, mark wangler -- >> when dateline continues.

>> on a cold summer day in early march 2011, dr. mark wangler, standing trial for murder, seem to want a moment with those for standing by him majoring ali can break from the trial. he showed us around his hometown, about an hours drive

from ohio. his old house is still there. history and brother-in-law on the family hardware store now. it was a strange homecoming. so much at stake. he seems so relaxed. >> i've been working here since 1970. >> okay. enough reminiscing. >> mark wangler wanted to see his mother, a chat and then goodbye. was it just for now four for good? >> i hope this isn't the last one. >> all right. >> i'm pretty confident. >> i am to. >> i'm feeling pretty good about it. >> even on this night before closing arguments, custer and mark fell to their routine, like choir practice at grace baptist. >> mark wangler never testified on his own behalf. would it matter? he was as quiet as ever and so hard to read. but not esther. she was a wreck, wondering what

will happen? what are the jurors thinking? in a courtroom back in line, closing arguments. defense attorney michael insisted that prosecution failed to make its case. >> did you hear them explain to you how dr. wangler allegedly committed this crime? no, you didn't hear any of that. you didn't hear any solid theory on that. >> it was an accident, he said. it was the water heater. >> they have failed to -- they just proven of the source, as a result, there is reasonable doubt. we must return the verdict of not guilty in this case. >> in his closing argument, prosecutor outlined his scenario for the jury. that he was convinced the doors all shut to create a direct pathway from the garage to the furnace to kathy's room. and then, start the car, or the

generator. or maybe both. >> and the water heater, it was checked over and over he said. sure there were code violations. >> you know, at that in keller. >> and then, the jury got the case. two weeks of testimony, much of it dense and scientific. what mattered most to the jury? >> you had expert testimony on both sides of this. >> right. >> did he come down to science for you? >> i don't think so. >> now. >> an afternoon passed and by the next afternoon, their verdict wasn't. esther was sitting with her son and mark's family. kathy's family was seated on the other side. >> we the jury empaneled and sworn to -- guilty of aggravated murder. [crying] >> dr. mark wangler was sentenced to life in prison, eligible for parole after serving 25 years.

>> mr. wangler, i you violated the ten commandments, thou shall not kill. you also violated the hippocratic oath. as a doctor, you shall do no harm. >> you remember the moment? >> yeah. i was shocked. the onset. i just fell and cried. i did think about it still. i don't cry. it's hard. i'll have one parent now. they took him from me. it's hard. >> we spoke with jury members both on camera and off. they said it was the simpler things that convinced them. the 9-1-1 call, the diary, the body temperature and the malfunctioning water heater? they didn't buy it. >> a couple of the other jurors

were very acknowledgeable on furnaces and hot water heaters. so, they gave their opinion of how they felt that it could have happened or could not have happened. >> you rolled out the water heater? >> pretty fast. within the first hour or two. >> to this day, do you have any idea how this crime might have been committed? >> i don't. >> no. >> no, ma'am. >> it was vindication for kathy 's family, especially her mother, who addressed the court. >> he's always been a very selfish person who really did not care about our beautiful daughter [inaudible] you are [inaudible] our family loved you, we always will love you and i hope someday we can have a connection like we had before. >> after his sentencing, mark's wife, esther, visited her husband in prison as much as possible. >> i just hope and pray that he doesn't get hurt.

or worse. >> detective says there were no winners in this case. he was only following evidence, he says, that led to a very sad conclusion about mark wangler. >> i think there is a lot of rage. although he wanted to live right where he wanted to have a good marriage, i think he couldn't. so -- >> you think he didn't see a way out? >> i don't think you saw a way out. >> that's all for this edition of dateline. i'm andrea canning. thanks for watching. ks for watching. ♪ ♪ ♪ >> welcome to morning joe weekend. it was an historic week for the country, as we follow the second indictment of former president trump.