CORPUS CHRISTI, Texas, Oct. 22, 2008— -- When 4-year-old Andrew Burd arrived at a hospital in critical condition in the fall of 2006, doctors didn't have a clue as to what was wrong with him. But blood tests soon revealed he had salt poisoning, or hypernatremia. Andrew's levels were off the charts: almost double the norm and among the highest ever recorded.
Doctors turned to Hannah Overton, a 29-year-old mother of four who was in the process of adopting Andrew. She told them Andrew had thrown a fit that afternoon after he'd been fed a full lunch. Instead of giving him more food, she said she put a few dashes of creole seasoning in a sippy cup of water.
But that didn't calm him, she said, and a few moments later he fell to the floor, vomited and complained of being cold. Hannah said she suspected the flu, but after an hour and a half, Andrew's condition didn't improve. That's when she and her husband, Larry, took Andrew to the hospital.
The Overton's story aroused the suspicions of doctors and investigators. The next day Andrew Burd died, and the devout Christian couple, who had no criminal history, became murder suspects. As the investigation continued, authorities developed a theory that Andrew's death was an intentional poisoning. Hannah and Larry Overton were soon arrested and charged with capital murder.
"This case boils down to a woman who, basically, tortured a child," said prosecutor Sandra Eastwood, "becoming so enraged she forced him to have 23 teaspoons of hot pepper, and then watching him die in agony."
The Overtons, backed by a community of fervent supporters, claimed there was a rush to judgment -- that the authorities had never considered alternate theories. The Overtons said that in the four months Andrew had lived with them, he had exhibited excessive tantrums and obsessive eating. They believe this unexplained behavior might have had something to do with his death.
"Something was wrong with Andrew. I don't know exactly how or what happened to him," said Hannah Overton. "Something caused his sodium levels to rise, and it wasn't me."
That was only the beginning of the story. To find out what happens, watch "20/20" Friday at 10 p.m. ET.