Melissa Elizabeth Lucio was born on June 18, 1969, in Lubbock, Texas. She lost her father when she was just an infant. When Melissa was a toddler, her family moved to the Rio Grande Valley, which is where her mother had grown up. As a child, Melissa faced difficult situations. She reported that she was sexually abused by her mother's boyfriend starting at the age of seven and this abuse lasted for about two years.

At the age of 16, Melissa got married to Guadalupe Lucio. Together, they had five children. She described her marriage as challenging because her husband was often addicted to drugs and alcohol, and he was physically abusive toward her. After that marriage, she had seven more children with Robert Alvarez. During her life, Melissa had a total of 14 children. Two of her children, who were twins, were born while she was imprisoned.

Mariah Alvarez was born to Melissa Lucio and Robert Alvarez in September 2004. On February 17, 2007, emergency services were called to the Lucio home because Mariah was unresponsive and not breathing. At the scene, medical personnel noted signs of abuse on Mariah, including bruises and a fractured arm. Lucio claimed Mariah had fallen down the stairs two days before her death. However, an autopsy revealed that Mariah had injuries consistent with blunt force trauma. She was pronounced dead at the hospital.

After Mariah's death, Melissa Lucio was arrested and interrogated for seven hours. During the interrogation, she stated that she had spanked Mariah but denied any abuse. After extended questioning, she said, "I guess I did it. I'm responsible." This statement was used against her in court as a confession. One of her sons was also interviewed, stating he saw his sister fall.

During the trial, medical experts testified that Mariah's injuries did not support Lucio's claim of an accidental fall. The jury found Lucio guilty of capital murder in 2008, and she was sentenced to death.

Following her conviction, appeals and retrials continued. In 2019, a federal court ordered a retrial due to interference with Lucio’s defense, but this decision was later overturned. In 2022, Lucio was set to be executed, but the Texas Court of Criminal Appeals granted a stay of execution, citing the need to examine new evidence of her innocence.

In subsequent hearings, evidence suggested that information that could have supported Lucio's defense was withheld during the original trial. In April 2024, a judge recommended that she receive a new trial, and the case returned to the Court of Criminal Appeals for further consideration.