April 23, 2009— -- Just days after the apparent suicide death of her second husband, 48-year-old David Castor, in 2005, Stacey Castor buried him in a rural cemetery in upstate New York. Lying next to him in the neighboring plot was Stacey Castor's first husband, Michael Wallace, who had died five years earlier, at age 38, of an apparent heart attack.
Police would later learn that it was more than coincidence that brought these two men to rest in neighboring graves. When police confirmed that both of Stacey Castor's husbands had died of anti-freeze poisoning, the grieving widow was thrust into the center of a murder investigation.
Stacey Castor, a tall, vivacious redhead, was introduced to Michael Wallace, the man she would call "the love of her life," by friends in 1985. Still a teenager at the time, Stacey said their attraction was instant.
"I knew five minutes after I met him that I was going to marry him," she told ABC News' David Muir in an exclusive interview.
The couple quickly became inseparable, and five years after their first date, they were married at Stacey's parent's home. Judie Eaton, Stacey's mother, recalled that her daughter was "as happy as she had ever been."
For Wallace, a gregarious guy who "liked to be the life of the party," having a good time sometimes meant using drugs and drinking too much, Stacey said.
"He had a problem with both for a long time in his life," she said.
But he also loved Stacey very much, and in 1987 the two welcomed their first daughter, Ashley. It was a life-changing moment for the new mother, who said the two "did everything together."
"I knew from that minute on, my whole reason for being here was to take care of her," she said.
Three years later, Stacey Castor gave birth to another daughter, Bree, and this time, it was her husband's turn to bond. He called their new baby girl his "princess."
Dani Colman, one of Stacey's oldest friends, recalled that Bree was "daddy's little angel" and that "she could do no wrong" in Wallace's eyes.
"There was no talk of any relationship between Ashley and Michael Wallace," Colman said. But Stacey said the connection between father and little sister was not lost on Ashley.
"I think it definitely hurt her," Stacey said.
She said that she made up for the father's slight by spending more time with her older daughter. The two became more than mother and daughter; they became "best friends."