Investigators said Horner had battered and strangled Athena to death.
Horner claimed that he had been possessed by his alter ego “Zero” and pleaded guilty to murder and aggravated kidnapping a day before the trial was scheduled to begin.
After two weeks of deliberations on whether he should receive life imprisonment or the death penalty, jurors said he should face execution.
Judge George Gallagher said that Horner would be executed “before the hour of sunrise” at a date to be determined, with the sentence carried out at the Texas State Penitentiary in Huntsville.
Elijah Strand, Athena’s uncle, addressed Horner during his sentencing. He said: “You will face the wrath of God. I want you to know you are a footnote in Athena’s story. Her name will forever be remembered.
“Her name will be forever celebrated, and everyone will forget you.”
Maitlyn Gandy, Athena’s mother, described her daughter as a “bright” girl who could often be found playing outside wearing princess dresses.
James Stainton, the lead prosecutor, said, Tanner Horner is proof why parents hug their children a little tighter.
“He’s proof of why children are nervous to go play outside. He’s proof of why there is evil in society, and we can never turn our back.”
Police and volunteers mounted a large-scale manhunt after her stepmother reported her missing at 6.10pm, two hours after the school bus dropped her off at her father’s house.
At one point during her abduction, Athena asked Horner: “Why are you doing this?”
He replied: “Because you are pretty.” Dashcam recordings showed Horner repeatedly threatening to hurt Athena if she screamed.
Police arrested him two days after the abduction.
During the police interrogation, Horner tried to bargain with detectives by offering information in exchange for being allowed to spend Christmas with his son. They refused.
Later that evening, Horner led police to the spot where he had taken Athena.
Jaqueline Ferrara, a forensic analyst, testified that male DNA was found on Athena’s body.
Two months after his arrest, a woman reported she had been sexually assaulted by Horner when she was a 16-year-old.
Two other women accused Horner of assaulting them when they were 16. He did not respond to the allegations.
Steven Goble, Horner’s lawyer, said in mitigation that Horner suffered from foetal alcohol syndrome disorder, a condition that causes emotional and cognitive problems, because his mother, a drug user and prostitute, drank heavily when she was pregnant.
After Athena’s death, Texas passed a bill known as Athena’s Law, which allows an alert to be issued to mobile phones, on motorway signs and on television and radio when a child goes missing, even if it is not confirmed as an abduction.
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