She was convicted of capital murder after the death of her two-year-old daughter, Mariah, who was found to have scattered bruising in various stages of healing, as well as injuries to her head and contusions of the kidneys, lungs and spinal cord.
Prosecutors said that Mariah's injuries were the result of physical abuse, while Lucio's attorneys say that her death was caused by a fall down the stairs two days prior.
According to the Cameron County District Attorney's Office, Mariah was found in her home with signs of abuse on her body, including marks on her back, missing patches of hair, and a fracture in her arm.
It was later determined that Mariah's arm had been broken two to seven weeks before her death, and an autopsy also showed a head injury and bruising of the kidneys, lungs and spinal cord.
[7] Following Mariah's death, Lucio was arrested and questioned for seven hours by Texas Ranger Victor Escalon without a lawyer present, and without receiving food or water.
"[10] During the trial, Lucio's recorded statements from her interrogation were described as a confession by Cameron County District Attorney Armando Villalobos, who was seeking re-election at the time.
[11][12] A pathologist, Dr. Norma J. Farley, testified that the child’s autopsy indicated that she did not die from falling down stairs, and instead her injuries were consistent with a death from blunt force trauma.
[14] Forensic pathologist Dr. Thomas Young, the former chief medical examiner in Kansas City, Missouri, reviewed the case at the request of Lucio's post-conviction attorney.
In the similar case of Manuel Velez, a man who was initially convicted for murdering a one-year-old baby and whose death sentence was overturned after further investigation, Farley's conclusions had also been contradicted by other medical experts.
They also argued that a judge's order to exclude expert testimony on the effects of trauma had "deprived Melissa of the only means she had of explaining that, notwithstanding her demeanor and self-incriminating statements, she was innocent of her daughter's murder.
[22] In April 2022, a juror on the trial, Johnny Galvan Jr., wrote in the Houston Chronicle that he had wrongly succumbed to peer pressure during deliberations and had changed his vote from a life sentence to the death penalty.
[9][23] The Mexican Ambassador to the United States, Esteban Moctezuma, announced on April 22 that he sent a letter to Governor Abbott asking him to grant executive clemency to Lucio, as "Mexico has historically manifested an unwavering commitment in its opposition to the death penalty.
[25] During the subsequent hearings, the District Attorney's office admitted that exculpatory evidence has been withheld at trial, and both sides requested that the court overturn Lucio's conviction.