The first hit from the aluminum baseball bat splits his skull. Then 11 more blows to the head and face finish him off.

Who killed Jason Corbett is no mystery. But why this unlikely pair did it is a huge controversy.

Was it self-defense or was it murder?

The story begins when a beautiful model named Molly Martens sees a nanny job a father had posted online. Molly lives in Knoxville, Tennessee. But the job is 3,700 miles away, in another country -- Ireland.

"She went to Ireland at age 24, you know, it's 'Do you wanna try something new? You wanna see a different part of the world, you wanna try a different career path,'" said Molly Martens' attorney Walter Holton.

Molly takes the job sight unseen and moves to Limerick, Ireland. She had never met the father, Jason Corbett, in person before she left Tennessee. Maybe she should have.

"She ended up with a man. He was older, he was very controlling, he was very abusive," said Holton. "And he was a classic abuser."

Jason Corbett needed someone to care for his two children after his wife Margaret died from a freak asthma attack.

"It was an opportunity for her, she went through the proper channels, she went through a screening agency and so forth," said Holton.

Jason was a big burly Irishman, who apparently loved to drink beer.

"He fit the profile of a person who outwardly, socially is the life of the party, as the happy-go-lucky guy," said Holton. "You know, as the happy drunk, he likes to drink but he's always happy. But inside the house it's different, and the children know. They were the ones who saw it."

Molly fell in love with Jason and with his adorable children Jack and Sarah. Their lives were upended when Jason's company transferred him to North Carolina. Shortly after they moved, Molly and Jason tied the knot.

"It looks like your traditional swept-off-your-feet love story," said WGHP-TV Reporter Alex Rose. "They basically get hitched, they come back to America with the kids, and Molly's parents aren't too far by, so they settle down in this little house."

Life in the $390,000 house in Winston-Salem seemed to be Nirvana. She worked as a swimming coach and doted on the kids.

"She loved those children, and he knew she loved those children," said Walter Holton. "They sent her Mother's Day cards for eight years saying 'Dear Mom.' They called her 'Mom,' he called her 'Mom.'"

Even though Molly was the only mother the children really ever knew, Jason wouldn't allow her to legally adopt Jack and Sarah.

"He had complete control over her. He didn't let her adopt the children, so she had no rights to the children," said Holton. "I think it was a control mechanism. I think he knew that as long as he had sole rights to the children that A), she wouldn't call 911, if he beat her."

If he beat her?

"She claims that they had a pretty tumultuous relationship between the two of them," said reporter Alex Rose. "She claims she had a little more confidence knowing that her dad would be there to protect her possibly, if it escalated."

Molly's father Tom Martens isn't the type who would sit back and watch his daughter get roughed up. He's a retired FBI agent and worked in counter-intelligence at the Oak Ridge National Laboratory, a nuclear facility outside Knoxville.

"Tom, of course spent his whole career analyzing crime scenes," said Rose. "His family described him as 'Wouldn't hurt a fly.'"

But what if that fly morphed into a monster -- a monster who Tom claims had to be swatted. With a baseball bat.

What happened inside the walls of that house prior to Jason Corbett's death?

"Sarah, the daughter, had woken up in the middle of the night, and she had awoken Molly," said Molly's attorney Walter Holton. "Mr. Corbett did not like the children coming into the bedroom for a variety of reasons, one of which is he would sleep nude.

"And he gets awoken, and he's very angry, he's mad at her for quote 'coddling the children.' He suffocated her, he attempted to strangle her, which he had done before. This was not the first time. And she screamed and her father came up," said Holton.

Tom says when he heard the screams, he rushed upstairs to the bedroom and found Jason had Molly in a death grip.

"He said 'I'm gonna kill her,'" said Holton.

Tom Martens just happened to have a baseball bat with him, an aluminum bat, a present he claims was for young Jack.

"Tom tried to get Corbett to let her go and he wouldn't do it," said Tom Martens' attorney David Freedman.

Tom claims he thought Jason, who weighed more than 260 pounds, was going to kill them both. So the present -- the bat -- became a weapon. Tom swings at Jason's head, again and again and again. Then Molly grabs a paving stone that she says just happened to be on the night stand. She smashes it into Jason's head. Twelve blows, and Jason Corbett was on the bedroom floor, naked, bloody and dead.

Even though Tom was just in a fight to the death, he sounded extraordinarily calm when he called 911.

Tom Martens: "My daughter's husband, my son-in-law, got in a fight with my daughter. I intervened, and, I, I think he's in bad shape. We need help."

911 Operator:: "OK, what do you mean he's in bad shape? He's hurt?"

Tom Martens: "He's bleeding all over. I may have killed him."

The 911 operator tells them to perform CPR on Jason.

911 Operator: "Is he conscious at all?"

Tom Martens: "No."

911 Operator: "Is he breathing?"

Tom Martens: "I can't tell."

Cops rush to the scene. When investigators arrived at the house in the middle of the night of Aug. 3, 2015, they weren't sure if this was a case of self-defense or murder. There was blood spattered on the wall more than four feet high. A photo of Molly detectives snapped shortly after the killing shows blood on her face. But where's the blood on her pajamas and hands?

Deputies take Molly and her dad Tom down to the station for questioning.

Detective: "OK, so you guys are arguing. OK. How is it physical? How does it become physical, what happens?"

Molly Corbett: "He started choking me and..."

Detective: "OK, where were you at when he was choking you?

Molly Corbett: "In the bed."

Cops take a picture of Tom in the shirt he says he was wearing and his boxer shorts. Remember, he did CPR. So why isn't he still drenched in blood?

Tom Martens: "I was scared to death that he was going to kill her, and subsequently I was scared to death that he was going to kill me."

Investigators begin to wonder. Was this really self-defense? Or was there a diabolical plot to kill Jason?

Molly Corbett and her father Thomas Martens have not disputed the fact that they delivered the fatal blows that took her husband Jason Corbett's life. But they claim it was all in self-defense.

Even the most beautiful house can hide the ugliest secret. And for former model Molly Corbett, that secret, she claims, was a husband with a violent temper.

Detective: "So there's a history of domestic violence at the house?"

Molly Corbett: "Yes."

Detective: "How long has that been going on?"

Molly Corbett: "Forever."

But forever came to a halt after Molly Corbett and her father Tom Martens bludgeoned Jason Corbett to death with a baseball bat and a paving stone. They claim it was self-defense.

Molly now finds herself in an interrogation room at the Davidson County Sheriff's Office in North Carolina telling her side of the story to detectives.

Detective: "How many times before tonight have you guys had physical altercations?"

Molly Corbett: "I don't know."

Detective: "Too many to count?"

Molly Corbett: "A lot."

Molly tearfully explains her version of events that led up to the bloodbath.

Detective: "Do you remember what you were fighting about?"

Molly Corbett: "My daughter had a nightmare. Um, she thought that the fairies on her sheet were insects and spiders and lizards. And he, I woke him, I woke up, she or I woke him up, so he was angry."

Detective: "You woke your husband up?"

Molly Corbett: "Yes, and he hates being woken up."

Detective: "So when he woke up, what happened?"

Molly Corbett: "I said 'She just had a nightmare,' I, I, he choked me, couldn't, wanted me to shut up, and I screamed. I was screaming 'Help,' and he was screaming 'I'm gonna kill you,' or 'I'm going to kill her.'"

In the middle of the interrogation, Molly did something odd, something so unusual that it caught the eye of the detective.

Detective: "Why do you keep grabbing your neck?"

Molly Corbett: "I'm sorry. It hurts. It hurts like on the sides and the back, and it hurts when I, when I talk."

Remember the picture of Molly in her mink coat taken just after the killing -- she appeared to be relatively unscathed by what she claimed was a choking attack.

Detectives take more pictures of Molly's alleged injuries in the interrogation room.

Detective: "Did you get that bruise?"

Molly Corbett: "Yeah, but it wasn't, it was from another night."

Detective: "Another night when?"

Molly Corbett: "Just when he grabbed my arm too hard."

Molly's part in the struggle was smashing a brick paving stone into Jason's head. She says there's a simple explanation about why it just happened to be in the master bedroom.

Detective: "You have a brick on the night stand?"

Molly Corbett: "Yeah."

Detective: "What was that for?"

Molly Corbett: "The kids and I are, were going to paint, paint these bricks and flowers around the mailbox."

Then the detective breaks the sad news to Molly.

Detective: "Um, you know your husband didn't survive his injuries, right?"

Molly Corbett: "I didn't, I didn't think so."

Detective: "All right, he didn't survive his injuries."

Down the hall, Molly's father Tom Martens was facing a separate team of detectives.

Tom Martens: "So I open the bedroom door and he's got Molly by the throat like this."

In a just-the-facts demeanor honed by three decades as an FBI agent, Tom calmly explains why he hit Jason with the aluminum bat.

Tom Martens: "And he goes around her throat like this, and I said 'Let her go,' and he turned and I hit him. A mean drunk. 'Let her go,' 'I'm gonna kill her,' 'Let her go,' 'I'm gonna kill her.' And he reaches out and grabs the bat, and he's stronger than I am, and he pushes me down and I'm scrambling on the floor, my glasses fall off. Now I'm thinking he's gonna kill me. And then I get the bat back. I don't know what happened while I'm down on the floor, and I can't tell you how many times I hit him, I can't tell you how many times he shoved me, and I can't tell you, I can't tell you, I, it's, it was battle."

The autopsy says Jason Corbett died from blunt-force head trauma. His head was so badly damaged that pieces of skull reportedly fell onto the medical examiner's surgical table.

Detective: "Was Jason drinking this evening?"

Molly Corbett: "Yeah, yes."

Detective: "Would you say that you thought that he was drunk?"

Molly Corbett: "Yes, he was drunk."

But according to the toxicology report, Jason's blood alcohol was only 20 milligrams per deciliter -- meaning he was 0.02 percent blood-alcohol content. Not legally drunk -- however, scientists say blood alcohol can decrease after death.

Molly Corbett: "I shouldn't have screamed."

Detective: "Why shouldn't you not have screamed? Didn't you need help?"

Molly Corbett: "Yes."

Detective: "Were you afraid for your safety?"

Molly Corbett: "Yes."

But something about their stories -- Molly's claims of abuse, an absence of blood on their clothing, and Molly rubbing her neck -- makes Davidson County, N.C. District Attorney Garry Frank wonder, are they telling the truth?

"She was I would say not frantic, but emotional, and kept rubbing her neck, even though there appeared to be no injuries to her neck," Garry Frank tells Crime Watch Daily. "The photographs that were taken of the two defendants, they had no injuries and not much blood on them. The photographs of the victim shows the profuse bleeding, blood all over the room, and it was just strange."

After the investigators are finished with their questions, Molly and her father are allowed to go home.

"You are not under arrest. As far as we're concerned right now, you're a witness," a detective tells Molly.

They may not know it, but they're not off the hook yet. Far from it.

Molly and Tom claimed they had no choice but to kill Jason in self-defense.

Tom Martens: "I know it sounds like an excuse, but I'm telling you, that guy was crazy . It wasn't just sloppy drunk. Something was wrong."

Something was wrong -- bloody wrong.

Prosecutor Garry Frank showed us the photos of Tom and Molly taken just hours after a killing so bloody we can't show them in their entirety.

"As you can see this is dried blood, but it's not her blood, it's a blood smear from something," said Frank.

They claimed they even performed CPR. So why weren't they covered in blood and bruises?

The investigation ramps up, and the prosecutor tells us the science doesn't match their stories.

"The EMT people that first arrived on the scene noted that the body seemed cool," said Garry Frank. "There were at least 12 blows to his head. Four of the blows in and of themselves would be incapacitating, and one blow post-mortem, so that is not consistent with a self-defense claim in our mind."

During his interrogation tom claimed Jason had Molly in a death grip.

Tom Martens: "And he's starting to drag her toward the bed into the uh, bathroom. And I hit him. I hit him in the head with the baseball bat."

Frank says if that's true then it would mean that the initial blows from the baseball bat hit him while he was standing up. But blood spatter experts found otherwise.

Does Garry Frank believe the blood spatter on the wall really told the story of this murder?

"I think it did," said Frank. "The blood spatter had indicated that it was close to the floor. In the area of a couple of the, blows the drops are going horizontal which indicates that the place of impact was low to the floor and the continuing spatter went across, horizontal. The deceased was low and down already when the main blows to the back of his head took place."

Shortly after the killing, a social worker interviewed Jason's son Jack, who backed Molly's claims of physical abuse.

Social Worker: "Did you see him physically hurt her?"

Tom Martens: "Once or twice.

Social Worker: "What did you see?"

Tom Martens: "Um, punching, hitting, pushing."

But later in the investigation, Jack, now in Ireland, is interviewed on Skype by North Carolina prosecutors. And he gives a bombshell admission. He says his statements were false.

Jack: "Molly made me lie to the people who were interviewing me."

Interviewer: "How did Molly make you lie?"

Jack: "Um, she made up a lot of stories about my dad, um, that he was, she said that he was very abusive and she wasn't lying."

So the bottom line: What could be the motive for murder?

"He had told members of his family that he was coming back to Ireland, going to bring the kids and go back to Ireland," said Garry. "And we believe that that's possibly a part of what precipitated this whole plot where this took place."

A grand jury indicted the pair on a charge of second-degree murder. The former FBI agent and his daughter were in handcuffs. Tom and Molly pleaded not guilty. Reporter Alex Rose was in the courtroom for the murder trial.

"You could cut the tension in that courtroom," said Rose. "One side has already lost a beloved family member, the other side potentially losing two people that they love in their family as well."

The jury didn't buy the self-defense claims and convicted them both.

"Molly's reaction was the sharpest in the courtroom. She broke out in a wail," said Rose. "Molly turns back to her mother and she says through choked-up tears, 'I'm sorry mom, I wish he would have just killed me.'"

In the loading dock at the back of the courthouse in Lexington, North Carolina, Molly and Tom in shackles climbing into the van that will take them to prison. But in the front of the courthouse, something strange is about to happen.

"One of the defendants, we didn't have any question as far as the participation. That was an easier vote. The other defendant we had to discuss," the jury foreman Tom Aamland told cameras.

What Aamland is about to say could dramatically alter the case.

"We didn't discuss a verdict, but in having private conversations, everybody, we could read that everybody was going in the same direction," said Aamland.

Private conversations are forbidden. Jurors are always admonished never to discuss the case outside the jury room.

"The defense claims they have a witness who saw the jury foreman and another juror go into a Nissan right after that first day of deliberation, after that first hour and a half, and they had a 10- to 15-minute conversation," said reporter Alex Rose. "You can only speculate as to what possibly happened in that car between 10 and 15 minutes. They could have been talking about Lexington barbeque for all we know."

Later Aamland doubled down on Facebook, posting: "... We decided on 2nd degree for both, but feel Molly was the aggressor, and her dad wanted to take the heat for her actions ..."

According to attorneys for Tom and Molly, that was forming an opinion based on facts not in evidence.

"It's very troubling for me, especially when I hear jurors make comments, 'Well, we felt it was overkill.' Well clearly you didn't listen to the instructions if that were the case," said David Freedman, Tom's attorney.

Tom and Molly immediately filed a motion for a mistrial based on alleged jury misconduct.

The judge disagreed: No mistrial. The conviction stands. Tom and Molly are sentenced to a term of 20 to 25 years in state prison. Their attorneys say they are appealing the mistrial decision.

Now Molly Corbett and her father Tom Martens are in separate prisons. They may never see each other again. At 67, Tom's sentence is so long it could mean he will die in prison.

And in Ireland, the littlest victims of this horrific killing, Jack and Sarah, lost their father, and now they have lost Molly, the only real mom they ever knew.

Jason Corbett's two children are now living with his sister in Ireland. They have recently filed a wrongful death lawsuit against Molly, her father and her mother. The suit seeks a total of at least $50,000 in damages.