"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.
"I would've done anything for her," Wallace said. "But she tried to kill me instead."
In 2000, Castor's first husband, the man she called "the love of her life," seemingly passed away from a heart attack. Wallace left Castor behind with their two daughters, Ashley, now 22, and Bree Wallace, now 19.
The bizarre death of Castor's second husband within five years of the death of her first husband made investigators suspicious.
Castor's death initially was thought to be a suicide by antifreeze poisoning. Stacey Castor buried him in a grave plot right next to her first husband.
Shortly afterward, investigators exhumed Michael Wallace's body and discovered traces of ethylene glycol, a chemical found in antifreeze.
What's more, forensic lab workers said the exact same chemical was found in David Castor's body.
Police concluded that Wallace also had died from antifreeze poisoning, and that both men had been murdered.
His eldest daughter, Ashley Wallace, was distraught.
"I started crying. I got upset," she recalled. "Why would they dig up daddy? Like, he was resting peacefully. I thought it was inhumane, and I didn't like it whatsoever."
Soon, Stacey Castor became the main suspect. Police wiretapped her telephone calls, and in a conversation with close friend Dani Colman, detectives heard Stacey Castor's worry and her denial of accusations.
"It scares the living [expletive] out of me because I didn't do this," Castor said in one of her phone conversations.
When the verdict was delivered Feb. 4, 2009, Stacey Castor was in disbelief. She was found guilty of second-degree murder and second-degree attempted murder.
"I think honestly that was the best day of my life," Ashley Wallace said. "Because I knew that people knew, I knew that they knew that I didn't do it."
Stacey Castor told ABC News she recalled thinking, "It can't be happening. It's got to be wrong."
She added that she believes she did not receive a fair trial.
"We weren't allowed to present a defense. There were things that were allowed in that shouldn't have been, things that should have been that weren't," she said.
After being asked repeatedly, Stacey Castor did not say what evidence or which witnesses would have altered the result of the trial.
Despite her denials, a judge sentenced Stacey Castor to more than 50 years in prison, the maximum sentence.
"In my 34 years in the criminal justice system, I've seen murderers of every variety and stripe, but I have to say, Mrs. Castor, you are in a class by yourself," Judge Joseph Fahey said at the sentencing. "What you did to David Castor can only be described as premeditated torture.
"Now, as bad and as evil as that is, what you tried to do to your daughter Ashley is simply something that I find I almost can't comprehend," he added. "I've seen a lot of defendants come through this court system, but I've never seen one who was prepared to sacrifice their child to shift the blame away from themselves."