'Half-Ton Killer' Reveals 800-Pound Weight Loss

Marya Roseles, 33, once weighed over 1,000 pounds and falsely admitted to murder.
3:00 | 12/03/13

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Transcript for 'Half-Ton Killer' Reveals 800-Pound Weight Loss
For one of the heaviest women in the world, shedding 800 pounds was just the beginning of a new lease on life. Texas prosecutors charged her with a crime that could have sent her to death row. Shedding weight meant shedding lig light on a dark family secret. On this week after thanksgiving, plenty of dieters are watching what they buy at the grocery store. No burger at all. This texas woman used ed d to weigh more than 1,000 pounds. She was one of the heaviest women on earth. How much weight have you lost? I have lost over 800 pounds. That's four good sized men taken all of your body? I used to take up a whole king sized bed. When a lot of people see you they think it's disgusting and hard to look at. What do you think? It's hard for me to look at it. I don't know how I survived that. Back in 2008, myra was not just facing death from obesity but from a lethal injection. She was charged with murder. This woman is almost half a on the. Why are my tax dollars keeping her alive. She was perhaps the most reviled woman in south texas, nicknamed the half on the killer. Why isn't she in jail? Charged with murdering her tiny nephew by falling on the 2-year-old. Myra is stating that she lost her balance and that she actually landed on the child, crushing his head. Her capital murder trial would be nothing short of a freak show. A defendant so big she had to be cut out of her house and transported in a moving van. And it cost so much to move her, her attorney even measured the courtroom -- the width is 130. And went shopping for a king sized mattress. We need to buy a mattress that will support over 1,000 pounds. So she could live in a courtroom while a jury decided if she lived or died. Myra admitted she killed the child but claimed it was an accident. We knew that myra was not being truthful. And suspected she was covering for someone. I tried to protect my sister. I was already dying. I was going to get capital murder charges. The death penalty. They were like doing me a favor. Myra lied for months but prosecutors started to doubt her when the little boy's autopsy revealed head trauma consistent with repeated abuse. In the face of that scientific evidence, myra finally told the truth, she'd seen her sister abuse her little boy and she even recorded her sister confessing. Right there. Right there. Jamie is accusing myra of testifying against her and myra said I didn't tell them how you hit him on the head with a brush. A logical person would say i didn't do it. She would acknowledge and wouldn't resist. Charges were dropped against myra and her baby sister was arrested on child abuse charges and now serving 15 years in prison. I was not doing right. I was willing to give up my life for her. Does she appreciate what you did for her? It's hard for someone to admit what they did, especially to their kid. And turn themselves in and confess. I think she because she could not live with herself no more with what happened. With her name cleared, myra moved to houston and began round the clock treatment from an obesity doctor. She's diabetic and has congestive heart failure. She probably is very close to going to respiratory failure. She lost 100 pounds. Next she endured a half dozen surgeries. Some to remove tumors and others excess skin. She adhered to a strict high protein diet. She had to lose 600 pounds just so she could safely have gastric by pass. Her transformation was filmed for a documentary on tlc. I think it's a miracle of god that I'm healthy and I'm alive. I'm not diabetic. I do not have high cholesterol or high blood pressure. It's possible just to take 800 -- subtract 800 pounds from somebody and they can walk around like normal and now you're okay? I'm okay. And my organs are perfect. That's crazy. I'm looking for clothes for job, something nice. These days the new and improved mayra occasionally gets reminders of her old life like letters from her sister. She showed me a recent one where jamie wrote that she wanted her to take care of the surviving children. She said that's why I want you to promise me please that if I am still in prison and something happens to our mom that you will take custody of my children. Mi rah visits those children often. Do you think you will be able to get custody of them at some point? I'm working on it. I'm in the process. She says the kids are the main reason she's still alive and her incentive to keep losing weight. They were the first to know when I was able to stand up for the first time. And then when they saw me walking and they saw me walk in the door they were very excited. Just to see you walking? Just to see me walking and happy. So they have provided a huge motivation? They are my motivation. A woman who has lost so much but somehow seemed to gain so much more. I'm ryan owens for night line in houston.

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

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