Mayra Rosales claimed she killed her 2-year-old nephew Eliseo Jr. when she accidentally rolled over and crushed him under her 1,100 pound frame.
But her lawyer knew something else was at play, according to "Half-Ton Killer," a new documentary that airs Oct. 10 on TLC.
In 2008, Rosales was living with her sister Jaime in Sullivan, Tex. In March of that year, Rosales now says she saw her sister use a brush to hit Eliseo repeatedly on his arms, legs and head, according to the Daily Mail.
Later that day, Jaime Rosales went out, leaving her sister to take care of her kids, despite the fact that Rosales was almost completely bedridden because of her weight. Eliseo Jr. started suffering from breathing problems that night. He was rushed to the hospital where he later died, according to the Mail.
Mayra Rosales decided to take the blame for the killing so that her sister's other kids "would still have a mom," her attorney, Sergio Valdez told Headline News this week.
Valdez says she never bought Rosales' original story that she crushed her nephew, especially after doctors determined the child's cause of death came from being hit, not from being smothered.
"We knew something was wrong from the very beginning," Valdez noted. "We said, we're going to have you reenact [how you killed the child] and you can show us."
However, when Mayra Rosales, now 31, was physically unable to demonstrate, "she broke down and started crying," said Valdez. "We knew she was covering up for somebody."
A press release from TLC, titled "Too Fat To Kill," notes that "Mayra could barely move." She was "deathly ill" from pneumonia and it required 10 men and an extra-large ambulance for her to reach the hospital when her health deteriorated later in 2008. She remains in the hospital today.
Mayra decided to come clean a few months later, after her sister continued to abuse her other children, according to Valdez.
Jaime Rosales ultimately pleaded guilty to causing injury to a child and is now serving a 15-year sentence.
"I’m really sad that my sister is in jail, " Mayra Rosales said, according to the Mail. "but I think my sister understands now that her actions were wrong. I believe she can change and learn from what happened."
See photos of Rosales below. WARNING: some images are graphic.