What former FBI agent, daughter say happened when her husband was killed

Thomas Martens, a 31-year veteran of the FBI, and his daughter Molly Corbett were found guilty of murdering her husband, Jason Corbett.
8:01 | 08/12/17

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Transcript for What former FBI agent, daughter say happened when her husband was killed
She was a loving and law-abiding family woman. Her father, a former FBI agent. Now both are facing decades in prison over the murder of her husband. A killing they say was in self-defense. Tonight they're speaking out about what they say happened that night with details the jury never got to hear. Here's ABC's reporter. Is your father guilty of murder? No. My father is guilty of saving my life. Tonight, Molly Martins core bet and her father Tom are convicted of second-degree murder in the death of Molly's husband, 39-year-old Jason Corbett. This morning a father and daughter in North Carolina are headed to prison. The father and daughter claim it was self-defense. They made for a rare pair of murder defendants. She had never broken the law, while he made a career enforcing it. Working for the FBI for 30 plus years. And yet, here they are enmeshed in a crime that has made news from the mountains of north Carolina to Ireland where nearly a decade ago, Molly took job as a nanny after an inquiry from a father in desperate need. Jason Corbett was emotional. He had lost his wife and there were two babies. Very quickly, their relationship goes from professional to personal. She back's mother to Jason's two kids. Then 3-year-old jack and 1-year-old Sarah. After three years together, Jason and Molly marry in Molly's home state of Tennessee. The wedding day, I have excited for them. The familiar little stays in the U.S. Moving into four-bedroom home. It was dream summer. Molly has it all, except one thing, Jason is refusing to make they are children's legal mother. I felt like he was going to follow through with the adoption papers. But that never happened. And Molly says there were other problems in their relationship. He was very controlling and very possessive. He would dictate what she should wear or shop for, when she should be home. Molly says the fights were escalating and the kids witnessed them. Later, son jack tells a social worker what he saw. He would physically and verbally hurt my mom. Molly says a lawyer told her to document any alleged abuse. Are you finished? I'm talking to you. Is this how you treat -- you just ignore me? She said she's caught between a rock and a hard place. Without a legal adoption, she has no shot of custody in the event of a divorce. I always came to the same conclusion that it wouldn't be better for them to lose a second mother. Tom Martins knows his daughter is suffering but decides she doesn't need another man bossing her around. I was not going to interfere in Molly's marriage. That was Molly's marriage. Two years ago that changed with Tom and Molly's mother were spending the night at the house. I don't know what precisely woke me up. What I heard were loud voices, like thumping. Something bad was going. On I grabbed that little league baseball bat and I ran upstairs. The bat was in his room. He had brought it as a gift for his grandson. What did you see? It's awful. He has his hands around her neck. He has her in a chokehold. Fear was secondary at that point. I was so ashamed that my father would see me like that. And I said let her go. And he said I'm going on kill her. Tom said he hit him in the head with a baseball bat but Jason kept dragging Molly toward the bathroom. Hit him hard in the back of the head again. You hit him hard. Yeah, did I. He still got her by the throat but he changed his tactics. He decides to come back at me. Jason just grabbed the bat away. Like it was nothing. Tom said he threw her to the ground. I was screaming, don't hurt my dad, don't hurt my dad. I thought, he's going to kill my father. I rush him and I grab the bat with two hands. Trying to hit him with the bat and he goes down. And then I realize, he is not going to get up. It looks like the threat is over. He's bleeding all over. I play killed him. With what? With a baseball bat. They tell the police it was self-defense. Just days after Jason's death, Molly begins fighting for custody of the children she's raised for eight years. While she's focused on Sarah and jack, the police have turned their focus to Molly and Tom. Dadeson county prosecutors say they took a hard look at these photos and noticed a vast difference between Jason's injuries and the absence of injuries they say on Molly and her father. They walked away with nary a mark on them. And he left on a board with his skull crushed and his scalp ripped off. Investigators say that bloody brick found in the bedroom is a key piece of evidence. In her police interview that night, Molly admits she hit her husband with it. I hit him on the head. With what? With a brick. Prosecutors become convinced Molly and her father are lying and charge them with second-degree murder and voluntary manslaughter. Are you guilty of murder? No. Did you murder your son-in-law? No. I didn't murder my son-in-law. And I would challenge any reasonable man, much less a reasonable father, to say that this was unnecessary forceful. During the trial he took stand and said he did what any father would do. You were defending your daughter. I was. I'm going to do everything that I have to do to save her life. But prosecutors tell jury to disregard Tom's testimony and focus instead on the blood spatter in the bedroom. They point to pictures like these, noting that most of the blood spatter is on the lower half of the wall with the area above relatively clean. Prosecutors say that demonstrates that Jason was still being hit after he was down. They challenged the notion that there was ever a threat that night. Floating a possible motive for murder that Jason may have been considering returning to Ireland and taking his kids with him. Molly's life was about those children and she wanted those kids. She was willing to kill for it? Maybe so. Defense attorney Walter Holten said Molly was the victim of abuse and there were two children in the house that knew it. And the jury didn't get to hear from they will. Mr. Corbett's family took children to pireland. They could have brought them back and let them testify. But during the trial, prosecutors read a statement from jack where he called Molly a murderer. And according to prosecutors, before the trial, they spoke to jack and this time he denied his father ever abused Molly. Afte nearly four hours of deliberation, they return a verdict. Guilty of second-degree murder. These jurors say they were convince in the part by the lac of injuries to Molly and Tom and they say they have a theory of their own about what really happened. I believe Molly made the first blow. Why? I believe Jason was in bed sleeping. And she struck him with the paver. And her dad help her cover it up? Out and help cover up. The judge sentenced both father and daughter on 20 to 25 years in prison. When I spoke with Molly, she told me that even before that sentence, she had already lost something more precious than her freedom. My life end that had day they took kids. For "Nightline," Lexington, North Carolina.

This transcript has been automatically generated and may not be 100% accurate.

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