(ABCNews)-- Mayra Rosales once weighed more than 1,000 pounds and was facing the possibility of a death sentence, not just from obesity but for the murder of her 2-year-old nephew.
But that was five years ago.
Today, the 33-year-old from Texas, who used to be one of the heaviest women in the world, now is one-fifth of her former weight, now weighing about 200 pounds, and her name has been cleared.
"I have lost over 800 pounds," Rosales said. "I don't even know how I survived that. It's a miracle of God. I really was dying."
Watch the full story on "Nightline" tonight at 12:35 a.m. ET
In 2008, Rosales was charged with murdering her sister Jamie's son. She was accused of falling on the toddler and crushing him under her bed. The case earned her the nickname "half-ton killer."
"I used to take up a whole king-size bed," she said. "I couldn't even stand up on my feet. My legs couldn't hold my weight."
Her capital murder trial was nothing short of a freak show, with the defendant being so big that she had to be cut out of her house and transported to court in a moving van. Her attorney even measured the courtroom and went shopping for a king-size mattress so she could live in the courtroom while a jury decided if she lived or died.
Rosales admitted to killing the child but claimed it was an accident. Her attorney never believed her claims and suspected she was covering for someone. That person turned out to be her sister, Jamie.
"I tried to protect my sister, and I was already dying so I didn't see ... like I was doing [something] wrong," Mayra said. "I was already giving up in life, and the way I saw it, when they began saying I was going to get capital murder charges, I really saw it like they were doing me a favor."
Rosales lied for months, but even prosecutors started to doubt her claims when the little boy's autopsy revealed head trauma consistent with repeated abuse. Faced with that evidence, Rosales finally told the truth -- that she had seen her sister abusing the child -- and she worked with her attorney to record Jamie confessing to the murder.
The charges against Rosales were dropped, and her sister was arrested on child abuse charges. She is now serving 15 years in prison.
"I knew I was not doing right, but I was willing to give up my life for her," Rosales said.
She added that her sister regrets what she did.
"It's hard for someone to admit what they did, especially to their kid, and turn themselves in and confess, and she ended up doing it," Rosales said. "I think she did it because she couldn't live with herself no more, with what happened, and because she knew I was covering for her."
With her named cleared, Rosales began round-the-clock treatment with an obesity specialist in Houston. In her first week, she lost 100 pounds. Then, Rosales underwent half a dozen surgeries, some to remove tumors and others to remove excess skin. She had to lose 600 pounds just to safely undergo gastric bypass surgery.
During the process, Rosales adhered to a strict, high-protein diet.
Her incredible transformation was filmed in a new documentary special for TLC, "Half-Ton Killer: Transformed," which airs on Wednesday, Dec. 4.
Before she started to lose the weight, Rosales said her organs were shutting down and now, after the weight loss, they are "perfect."
"I think it's a miracle of God that I'm healthy," she said. "I'm alive, and I'm not diabetic. I do not have cholesterol [problems]. I don't have high blood pressure, so I'm healthy."
Sometimes, Rosales said she would occasionally get reminders about her old life, such as when sister Jamie sends her letters from prison. In one letter, Rosales said Jamie wrote that she wanted Rosales to take care of her surviving children, who now live with Rosales and Jamie's ailing mother, if the mother dies while Jamie is still in prison.
Rosales said she visits Jamie's kids often, and that the children call her "mom." She said she is in the process of getting custody of them, and that they are her incentive to keep losing weight and stay alive.
"They were first to know when I was able to stand up for the first time, and then when they saw me walking, they saw me walk in the door, they were very excited," Mayra said. "They are my motivation."