Dateline NBC - Deadly Exposure

Episode Date: June 22, 2021

Accidental carbon monoxide poisoning is the cause for hundreds of American deaths every year, but according to police in Lima, Ohio, one of those deaths wasn’t an accident – in this Dateline classic, they say it was murder. Kate Snow reports. Originally aired on NBC on June 24, 2011.

She was a wife. She was a mother. She was the most amazing woman I've 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 a 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 in gases. He's an anesthesiologist. Did you kill your wife, Kathy? Thanks for joining us. I'm Lester Holt. Hundreds of Americans die every year from accidental carbon monoxide poisoning. But according to police in Ohio, one of those deaths wasn't an accident. It was murder. And they say if anyone would know how to use a deadly gas to murder someone, it was their prime suspect. Here's Kate Snow.

He's come back to where it all began, to the town, 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 monoxide detector has gone off, and my wife's having a seizure. Our story begins in Lima, Ohio, on a frantic pre-dawn morning, September 4, 2006. Dr. Mark Wangler says he woke suddenly in the downstairs master bedroom to the sound of an alarm. What kind of alarm? Just a loud piercing noise

and was able to determine that it was the carbon monoxide detector. Then I ran to check on Kathy. Kathy Wengler was 48 years old and for most of her life had suffered from epilepsy. She was sleeping upstairs. I went in and shook her and called out to her, screamed at her, but she wasn't responsive. I call 911. And you tell them that she's 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 she have a heartbeat? No, she doesn't. Do you remember doing CPR? Yes, I do remember doing the CPR. I'm starting CPR. Okay.

Next door neighbor, Diane Stuber, saw the rescue squad at the Wangler's home. So I went over and I said to Mark, Mark, did Kathy have a seizure? And 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 Lima Memorial Hospital. Mark followed along, and Diane Stuber 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 that 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, but as a doctor, Mark Wangler says he knew he had been poisoned with carbon monoxide because his head hurt and he felt so disoriented. Neighbor Diane Stuber says she remembers

how Mark took the news of Kathy's death. He sobbed like a baby. The tears were rolling down his cheeks, and he was just like, you know, this. He couldn't believe that it had happened. I wanted to see Kathy's face. I wanted to see Kathy. To say goodbye? Yeah, it had happened. I wanted to see Kathy's face. I wanted to see Kathy. To say goodbye.

Yeah, it was tough. Kathy's family members drove to Lima 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 and It's hard to see your parents cry. And then turn around and call your brothers and sisters. Mark Wangler called his two sons, Nathan and Aaron, who were living in Cincinnati. Aaron was in his second year of college. I just remember just screaming and crying. It was horrible. The brothers rushed home to their father in Lima. I remember him and my brother and I just holding each other and all this just like sobbing and crying and like his body was like shaking from crying so hard like. Thousands of people are

accidentally poisoned with carbon monoxide every year. It usually happens when something like a space heater, a furnace, or a water heater malfunctions. Investigators wanted to find out quickly what went wrong at the Wangler home, so a detective came to speak with Mark Wangler at the hospital. Former Allen County Sheriff Sam Krisch ran the detective bureau back then. He says Dr. Wangler mentioned the water heater. Dr. Wangler made a comment that they were having problems with this water heater. In the past few weeks, the flame would go out occasionally

and felt that that was the problem due to the carbon monoxide detectors going off. Diane Stuber remembers her husband worried about the Wangler's water heater too, saying the exhaust pipe on the roof wasn't placed there correctly. Could that have caused a backup of carbon monoxide into the house? And he told Mark, I said, that would scare me to death, Mark. It sounded like Mark Wangler was lucky to be alive. Kathy just happened to be the one sleeping upstairs that night. Mark was downstairs. It seemed like a sad but explainable accident. But as it turns out, it wasn't so simple. Coming up, growing suspicions that something was missing.

We walked around the house. We looked at the water heater. We looked at the other appliances. We just couldn't find a source. For the carbon monoxide? Right, because the appliances appeared to be working properly. When Dateline continues. 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. For her sons, Nathan and Aaron, it was devastating. As Aaron told us, they adored their mother. She was amazing. The most amazing woman I've ever met in my life. Did everything for everyone. Always put herself last.

Always put my brother and I number one priority in her life and my dad. And she certainly didn't want to be defined by her epilepsy. It started when she was a little girl, but medication seemed to keep it under control for the most part. Kathy was 15 when she met Mark Wengler. I grew up in a little town of Fort Recovery, Ohio. It's in about the middle of the state, down near the Ohio-Indiana border. Small town of about 1,200 people. What was that like?

I enjoyed it. I really loved growing up in a small town. We played softball in the backyard and knew all your neighbors. You knew everybody in town, and everybody 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 come in, they go, Mark's here. I go, Mark who? And they said, Mark, that Wagner guy. And I said, where's he at? And he was out, he brought his guitar, and he came and sat on the back seat, back of his vehicle, and he was strumming a guitar, singing to Kathy.

Serenading her? Yes. Yeah. They started dating, and a few years later, in 1977, Mark and Kathy got married. He was 21. She was 18. They held their wedding in a Catholic church, but by then, Mark had embraced an evangelical Christian faith. They were as happy as two people I've ever seen. And it turns out the quiet young man from Fort 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? Yes, it was. It was a good marriage. You had two boys. Correct. Nathan and Aaron were born right as Mark was beginning his practice.

We were the family that you would give hugs and kisses every morning and every night before you go to bed and when you leave for school or even if you were just going out to go hang out with your friends or wherever. We always kissed and loved. We were always like a very close family. They moved to Lima in 1990, and by then the Christian faith had become very important to Mark Wengler. They joined Grace Baptist Church. What was it about this particular church that you and Kathy both thought was a right fit?

Two things. One of them is we felt that the people there were friendly, and the pastor was correctly preaching God's Word. And the second thing is that they had a very active children's program or 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 Wanglers. Next door neighbor Diane Stuber was fond of both Kathy

and Mark. Mark was more reserved. Nice man, very patient and caring person. Would help you out, do anything for you. And you know he had his little peculiar ways about him. He was a little dorky and he looked different from other people until you get to know Mark and he is the most wonderful person that you could ever meet. Kathy was a lot of fun to be around. She was bubbly, she had a crazy laugh, loved life, just a lot of fun. But 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 checked that out. And the Allen County prosecutor was concerned by what they didn't discover. Prosecutor Juergen Waldick often examines the scenes of unexplained deaths in Allen County. We walked around the house, we looked at the water heater, we looked at the other appliances, the gas furnace, the gas logs, the garage, and also the bedroom where Kathleen Wengler died. They couldn't find a problem with any of the appliances.

We just couldn't find a source. For 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, he said, but 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, but some members of Kathy's family weren't ready to move on. They were still asking questions, and they thought the answers just might lie with Mark Wangler. Coming up. And 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 and Kathy was driving away yelling at him. When Dateline continues. Kathy Wengler's death certificate said 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 really wanted to talk about it, and it, you know, the police weren't calling us. I felt as if nothing was getting done. So Diana decided she'd had enough.

So I actually called Mom, and she actually called the sheriff's department. And 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. Because they knew something. The Wangler marriage was a disaster, and they wanted police to know the problems went back years. What Kathy had told me is basically Mark had an affair.

That can't have been easy for your sister. She could never ever forgive him for that. They managed to carry on, but 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 a big family gathering. Mark and Kathy were fighting again. She got in the car. The boys got in the car. Mark was hanging on the side of the car, and Kathy was driving away, yelling at him. And 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 Wengler admits things did go downhill after the boys left for college. He says Kathy would get deeply depressed. With the boys being gone, she kind of Kathy would get deeply depressed. With the boys being gone, she kind of lost her purpose in life, I would say. Were you working on it? Were you trying to? Yeah, we were in counseling. And then 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 opened. That was because the toilet in the master bathroom

had 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 months after Kathy died, her case file landed on the desk of a veteran detective,

Clyde Breitigan, since retired. What's your instinct? In reading the reports, I was sure that the water heater, the furnace, and the vent-free gas fireplace were not the source of the carbon monoxide. So then you have to think, okay, what else in that house could produce carbon monoxide? There was a generator in the garage, there was two cars in the garage,

there was a snowblower in the garage. Those all produce carbon monoxide. But of course, all 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 Breitigan knew it sounded improbable,

but he kept thinking about the logic of that other detective, Sherlock Holmes. It was a matter of just eliminating the impossible things, and at the end you're stuck with the improbable. And there's another clue Breitigan and the Allen County prosecutor couldn't ignore. Dr. Mark Wangler had a specialty. I mean, he's an expert in gases. He's an anesthesiologist. That's right, an anesthesiologist, a doctor who knows exactly how to put people to sleep. Did he use his expertise to kill his wife? an anesthesiologist, a doctor who knows exactly how to put people to sleep.

Did he use his expertise to kill his wife? In April of 2007, seven months after Kathy's death, Detective Breidegen got a search warrant for the Wangler home. He had a videotape running as officers seized a computer, papers, and Mark's journals. Detective Breidegen says the journals really caught his attention. You'd have to read the whole thing, and I cannot explain that. I wish I could. It's just that he was at like the end of his rope, and I think he felt trapped. But now, all these months later, Mark Wangler's life was on the upswing. He had reconnected with an old friend who shared his faith, Esther Van Dyne. A romance blossomed.

You ended up getting married, I think, about a year after Kathy's death. Fourteen months, correct. Some people might think that that's pretty fast, to bounce back. Yeah, we've heard that. And the wedding bells had barely stopped ringing when Detective Breitigan got a second search warrant. Because by now, he had come to believe that Mark Wangler was a killer. Breitigan thought that Wangler had 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. And we went in and dismantled the ductwork and took carpet samples and the registers out of the house. Investigators found a lab that would try to determine if soot from an internal combustion engine could be found inside the heating ducts. It would be months before they got results. Did you have any idea that as you were having this busy, happy time, investigators were still trying to put a case together? We really didn't hear anything for a long time. Yeah, we didn't hear anything at all for a long time. So you plan 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 fresh water, 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. Yeah. And your son calls. He said, do you know some guy named Bright again? They were banging on the door. That's the detective? Yeah. So you knew then? So we knew then in the Atlanta airport that there

must have been an indictment and they were at the door to arrest Mark. The lab results were in on that ductwork. Coming up, the prosecution's case, motive. We have some diaries that are pretty dark and kind of lay out what the state of the marriage was. And means. Can you tell the jury what, if anything, you noticed in that particular bedroom?

I observed soot-like marking on the wall directly above the register, the heat register in there. When Dateline Continues. On September 19, 2009, as Mark Wangler boarded a plane from Atlanta to Ohio, he knew he was about to be charged with killing his first wife three years earlier. I felt that 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 at the Allen County Courthouse. Prosecutor Juergen Waldick didn't have fingerprints, DNA, or an eyewitness, but he believed the

evidence would show that Dr. Mark Wangler killed his wife while she was sleeping using engine exhaust containing deadly carbon monoxide. I have someone who's died of carbon monoxide poisoning. Really high levels, 69%. I have a defendant who has really low levels. We have no legitimate source of carbon monoxide in the home. And we have some diaries that are pretty dark and kind of lay out what the state of the marriage was. And that's 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 Mark criticize Kathy on the topic of money? Yes, he didn't like her shopping. Prosecutors suggested Mark had become increasingly angry about his wife's spending. Just after Kathy died, Mark showed investigators cash, jewelry, and credit cards he found in Kathy's car. So why not divorce? Friends and family testified Kathy wouldn't leave the marriage because she was afraid Mark would cut off her money. As for Mark?

The defendant was deeply obsessed with religion, and a divorce would cause him to lose his standing and reputation in the church. And if Mark and Kathy were stuck with each other and fighting all the time, his journals painted an even bleaker picture. The man who wrote them wasn't just unhappy, he was depressed, and according to prosecutors, desperate enough to kill. Detective Breitigan took the jury through each painful entry. I am tired of her lies and hiding a 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 me from within my own family. Just two months before Kathy Wangler died, Mark wrote this. Thoughts of suicide are a little strong again. Satan is attacking in a new way this time, using car exhaust. That's a real red flag. It tells you the state of someone's marriage, at least in our assessment, that if your marriage is so bad that you're willing 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. In the eyes of prosecutors, a motive. And that 911 call raised even more suspicion as far as the prosecution was concerned. I'm still here, sir. Okay, well, I'm trying to breathe for you. Okay, that's fine.

Okay, thanks. I'm starting CPR. Okay. It just didn't sound like he was doing CPR on the 911 call. It sounded like the whole thing was staged. And if Dr. Mark Wangler was doing CPR, why would 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's basic CPR. But something even more important crossed the chief's mind after he found Kathy, and this was a huge red flag for prosecutors. He said Kathy's body was cold to the touch, odd since Mark told 911 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 have been unusual for someone who had just minutes before quit breathing and heartbeat. That's correct.

The ER doctor backed him up on that. She had a rectal temperature that was quite low. My documentation is that it was like 94. The doctor also testified the body seemed to be getting stiff. It seemed like she'd been dead for a while. In other words, dead before her husband called 911. 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.

In the days that followed Kathy's death, investigators tested and retested the water heater and other appliances. Prosecutors reminded the jury 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 the heating vents except the ones in Kathy's room. Then he must have shut the doors to the furnace room, except for the one leading to the garage. He could have started a car or a generator or maybe both and filled the garage with carbon monoxide. The carbon monoxide would then find the only open path down the stairs

into the furnace. The deadly gas would then travel through the heating ducts and out the vents in Kathy's room. They pointed to pictures taken of Kathy's room after she died. Can you tell the jury what, if anything, you noticed in that particular bedroom? I observed a soot-like marking on the wall directly above the register, the heat register in there. Nobody actually tested that stain on the wall before it was painted over, but prosecutors were prepared to show that engine exhaust had come through the heating ducts and out those vents.

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 a reasonable degree of scientific certainty that the exhaust from a combustion source was directly introduced into the ventilation system? Yes. And can you say to a reasonable degree of scientific certainty

that the water heater was not the source of the soot in the ventilation system? Yes. Devastating for Mark Wengler's case? Maybe. Maybe not. Coming up. Ladies and gentlemen, 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 that you may even find that the water heater did this.

But 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. All that time, his sons stood by him and against their mother's family. When you have your family stabbing you in the back and trying to destroy your own family of 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. In his opening argument, McDowell said Mark was, above all, a devoted Christian who would never commit murder. Mark did not believe that it was good enough just to profess the words of Christ or to go to church. He felt that he had to live it. Mark Wengler's defense came down to this.

His wife died in a horrible accident. The prosecution never proved a crime was even committed. Ladies and gentlemen of the jury, Dr. Mark Wengler is innocent. This case has been brought as a result of a 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 and could have sent carbon monoxide into 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? You face up to the rest of your life in prison. I try not to, for the most part. Sons Aaron and Nathan provided key testimony. How would you describe your father? A great man, 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 Aaron and Nathan said they believed their parents really did love each other. Up to the day of her death, do you believe that your father loved your mother? Absolutely. And then the defense turned to the Mark Wangler journals with their depressing entries about the marriage. The defense challenged the detective. Didn't the diaries portray a man working on his marriage? Mark prays for a good relationship with his wife, correct? Yes, he does.

And he prays that his wife will also sort of see the way and work on the relationship too, 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 911. But the question was, when exactly did that poisonous gas kill her? The prosecution had argued she was already dead when her husband called 911 because her body was so cold. But how cold was it?

Apparently, the ER doctor got the temperature wrong. This is the nurse's handwritten notes indicating that the body temperature, the rectal temperature is actually 1.5 degrees more than what you had written in your other notes. Is that correct? Is that yes, ma'am? Yes, yes, I'm sorry. Okay. Yes.

So Kathy's body wasn't as cold as the doctor thought. Considering this, a leading forensic pathologist testified her heart could easily have stopped exactly when Mark Wangler said it stopped, during the 911 call. The defense also had to knock down evidence from the Wisconsin lab. You remember, the lab experts said they had found soot inside the Wangler's heating ducts that came from engine exhaust. This is junk science as applied to the facts of this case. McDowell said other bigger reputable agencies like the FBI and the Ohio State Criminal Lab refused to do the testing.

It was too unreliable. These people at Wisconsin said, we've never done it before, but we can try it. McDowell attacked the lab's data, its record-keeping, and its expertise. Prior to your work and 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? 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 a potential source of soot, correct? Yes, that is correct. Candles. The Wangler house was full of them, according to testimony from several witnesses like son Aaron Wangler. Maybe that's why the heating ducts were full of soot. Do you recall if your mother ever burned any candles in the home here?

All the time. We had tons of candles. And remember those soot stains coming out of the registers in the room where Kathy died? That was Aaron's old room. Those marks were actually there before I moved for college. So that was back in 2004. The defense said the prosecution's murder scenario involving vehicle exhaust and the furnace was preposterous. It had to be the simple explanation. Kathy's death was an accident. And now came the most important testimony in the defense's case. An environmental toxicologist testified the most likely source of carbon

monoxide was the water heater. What was the closest source of carbon monoxide? The gas-fired water heater in the basement of their home. I think, 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 was in a sealed cabinet. 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 vent cap 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 that you may even find that the water heater did this. But regardless, you will not find that Dr. Wangler murdered his wife because he did not. Coming up. You had expert testimony on both sides of this. Right. Did it come down to science for you? I don't think so. The verdict.

We, the jury, being duly impaneled and sworn by the defendant, Mark A. Wangler. When Dateline continues. On a cold Sunday in early March 2011, Dr. Mark Wangler, who was standing trial for murder, seemed to want a moment with those who were standing by him. During a weekend break from the trial, he showed us around his hometown, about an hour's drive from Lima, Ohio. His old house is still there. His sister and brother-in-law own the family hardware store now. It was a strange homecoming with so much at stake. He seemed so relaxed.

I haven't worked in here since 1977 and there's some of my printing. Okay, enough reminiscing. Mark Wengler wanted to see his mother, a chat, and then goodbye. Was it just for now or for good? I hope this isn't the last one. I hope I get to come back. I'm pretty confident. Well, I am too. I'm feeling pretty good about it.

Even on this night before closing arguments, Esther and Mark held to their routine, like choir practice at Grace Baptist. Mark Wengler 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 Lima, closing arguments, where defense attorney Chris McDowell insisted the 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, really hear any solid theory on that. It was an accident, he said. It was the water heater. The government has failed to disprove it as the source. As a result, there's reasonable doubt. You must return a verdict of not guilty in this case. In his closing argument, prosecutor Juergen Waldick outlined his murder scenario for the jury. The heating vents, the doors, all shut to create a direct pathway from the garage to the furnace to Kathy's room.

And then he started the car or the generator or maybe both. And then he waited. And the water heater? It was checked over and over, he said. Sure, there were code violations. But you know what? That didn't kill her. 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 it come down to science for you? I don't think so. An afternoon passed, and by the next afternoon, their verdict was in. Esther was sitting with her son and Mark's family.

Kathy's family was seated on the other side. We, the jury, being duly impaneled and sworn fine, the defendant, Mark A. Wangler, guilty of aggravated murder. Dr. Mark Wangler was sentenced to life in prison, eligible for parole after serving 25 years.

Mr. Wangler, you violated the Ten Commandments. Thou shall not kill. You also violated the Hippocratic Oath. As a doctor, you shall do no harm. Do you remember that moment? Yeah, I was shocked, but just beyond sad, I just bawled. And I cried hysterically. And, I mean, thinking about it still, like, makes me want to cry because it's hard, you know. I'd like, I only have one parent now, and they took him from me. So, it's hard.

We spoke with jury members both on camera and off. They said it was the simpler things that convinced them. The 911 call, the diary, the body temperature, and the malfunctioning water heater. They didn't buy it. Eldon and a couple of the other jurors were very knowledgeable 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 ruled out the water heater? Pretty fast, I think within the, what, first hour or two.

To this day, do you have any idea how this crime might have been committed? I don't know. No, ma'am. It was vindication for Kathy's family, especially her mother, who addressed the court. We know you have always been a very selfish person who really did not care about our beautiful daughter, only yourself. Nathan and Erin, you are our first two grandchildren.

Our family love you. We always will love you. And I hope someday we can have a connection like we had before. Our first two grandchildren, our family love 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 Breitigan 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 was a lot of rage in him, and although he wanted to live right, or he wanted to have a good marriage, I think he couldn't. You think he didn't see a way out? I don't think he saw a way out. That's all for now. I'm Lester Holt.

For all of us at NBC News, thanks for joining us.