"The only physician that treated Andy while he was alive, and who was aware of the other neurological problems that he had, was me," Cortes said. "And I think that testimony might have given the jury an understanding that perhaps he was not a totally normal child."
But neither the defense nor the jury ever heard Cortes' opinions, which are the cornerstone of Hannah's appeal.
Prosecutor Sandra Eastwood said she doesn't recall Cortes expressing doubts about Hannah's intent.
"Sounds very disingenuous," Cortes told "20/20," "I was very clear from day one and very forceful as to my opinions."
Overton's appeal alleged that the state withheld Cortes' opinion from the defense. But in the appellate decision the court said, "Because there is conflicting evidence regarding whether the state knew of the alleged exculpatory evidence, we cannot conclude that the information was in fact known to the state or that the state was required to produce the unknown information."
The court added that even if Cortes had expressed his doubts to the prosecution, the state "has no duty to disclose inadmissible evidence." And that "Texas courts have repeatedly excluded expert testimony regarding a defendant's state of mind or intent at the time of the offense because it is speculative and unreliable."
Yet, in an earlier section of the decision, the court points to another prosecution expert, Dr. Alexandre Rotta, who testified that he believed Andrew was given the creole seasoning and water mixture after he had a temper tantrum "probably to punish his behavior."
In a 2008 interview with "20/20," prosecutor Eastwood stood by her case. "I feel very confident that I did the right thing in presenting the evidence and having her convicted," she said. She also remains convinced that Hannah Overton knew or should have known that withholding medical treatment would kill Andrew.
"I think she was angry, enraged, with wanting to punish him and hurt him and then realized, 'Oh my gosh, I've really hurt him.'"
Dr. Michael Moritz, a leading expert on salt poisoning at Children's Hospital of Pittsburgh, said, "I don't think there was any evidence at all that she did this."
Hannah's defense team hired Moritz but never put him on the stand, believing his testimony would be repetitive. Moritz believes he knows what happened to Andrew.
"I think he was in one of his feeding binges. He was having a tantrum, and he was unsupervised for a brief period of time, and I believe that he ingested a large amount of salt."
Moritz has written extensively about salt poisoning and its connection to pica.
"When I pulled all the cases of salt poisoning, they all fit the same profile," he said. "Children within that age group of 2 to 6 years of age, in foster care from abusive homes but with behavioral problems, who had history of pica, who by all accounts appeared to have voluntary ingested large amounts of sodium."
For his part, Moritz doesn't believe Hannah Overton knew Andrew was dying.
"I think most people would never suspect salt poisoning, since it's something very few pediatricians or emergency rooms in the country have ever encountered," he said.
Since Hannah Overton's trial concluded, her husband says he's tried to take things day by day.