"I did not kill David Castor," she said in an exclusive interview with ABC News' David Muir. "And I did not try to kill my daughter, period. And I will never say that I did. Ever."
In January, Stacey Castor stood before a judge and jury in the Onondaga County courthouse in Syracuse, N.Y., where she was given the chance to plead her innocence. Jurors listened to the testimony of more than 50 witnesses and deliberated for three days.
She was accused of murdering her second husband, David Castor, by poisoning him with antifreeze in 2005, and attempting to poison her daughter, Ashley Wallace, with a toxic cocktail of crushed pills and vodka. She also was suspected of murdering her first husband, whose grave lies next to David Castor's.
"I think she's diabolical," said assistant district attorney Christine Garvey. "What she has done over the course of seven years is just unimaginable."
Stacey Castor's defense attorney, Chuck Keller, said, "It's a tragedy for everybody. No matter how it comes out ... it's a tragedy. ... There is no happy ending.
Keller hopes the jury will find reasonable doubt.
"They can't take someone's life away when there is a chance that they've got the wrong person," Keller said.
Castor's case was Keller's first murder trial, and he spent almost two years digging up a trail of evidence that, he said, pointed to a different murderer: Stacey Castor's 21-year-old daughter, Ashley.
In court Stacey alleged that her daughter Ashley had murdered both Michael and David.
If Ashley had indeed been responsible for Michael Wallace's death, it would have meant that she killed her biological father by poisoning him with antifreeze at the age of 11.
"It may be easier for people to decide that I did it because I'm the mother," Stacey Castor said. "But kids do things like that. All you have to do is turn on the news or read the paper. There are children that kill children and other people every single day. It happens."
Castor hasn't spoken to either of her daughters since she was arrested at the hospital after Ashley Wallace nearly died in September 2007.
"You know, the truth will come out," Castor said. "I know that the truth is going to come out of this. The evidence will show that I am innocent. And I will go home."
Wallace maintains, along with investigators, that Castor not only killed David Castor, but also killed Michael Wallace, who was Ashley Wallace's father and Stacey Castor's first husband.
Wallace now believes her mother tried to frame her for the deaths of both men.
But Wallace was confused, saying she never had written a note, and she hadn't taken any pills.
"It's just bald-faced evil," District Attorney William Fitzpatrick said. "[Ashley] almost died. She probably came within a couple of doses of Lexapro of dying. No one that I've ever prosecuted was so coldblooded, so heartless as this woman [Castor] was -- and so unemotional about it."
Wallace told ABC News that her mother once was her best friend, but that they have not spoken since the day of Castor's arrest.