Exclusive: Mother and Daughter Face Off in Murder Mystery

April 22, 2009— -- Stacey Castor wanted people to believe that she was simply an unlucky wife after her first husband died of an apparent heart attack in 2000 and her second of an apparent suicide in 2005 by poisoning himself with anti-freeze.

But sympathy for Stacey Castor turned to suspicion after the exhumation of her first husband Michael Wallace's body proved that, like David Castor, he too died of anti-freeze poisoning. And in a bizarre twist, Castor eventually also became a suspect in the attempted murder of her own 20-year-old daughter, Ashley Wallace.

"She was my best friend," Ashley Wallace told ABC News' David Muir in an exclusive interview. "She was, and then she took that all away. I would've done anything for her. But she tried to kill me instead."

Soon after the September 2007 discovery that both of Stacey Castor's husbands had been poisoned, detectives Dominick Spinelli and Valerie Brogan of the Onondaga County Sheriff's Department paid a surprise visit to Stacey's residence in the small town of Clay, N.Y., outside Syracuse.

She was taken to police headquarters and questioned about the deaths of her husbands, adamantly defending herself with her version of events and insisting that on the day David Castor allegedly committed suicide, she repeatedly called their home to check on him. But when Spinelli told Stacey that phone records showed she had in fact called only once, the three-hour interrogation abruptly came to an end.

"She was getting anxious, and she shut down and said, 'That's it. I'm done. I want an attorney,'" Brogan recalled.

At that point, detectives believed that Stacey Castor, now 41, panicked and searched for an escape.

Ashley Wallace, Stacey's older daughter from her first marriage to Michael Wallace, said she was outraged and shocked to learn that her mother and best friend was a murder suspect, and said she even told her mother something that would later come back to haunt her.

"I wish that I had done this so they would take the focus off you and it would put the focus on me," she recalled saying.

As detectives listened to Stacey's wiretapped phone calls in the days following her interrogation, two detectives showed up on Ashley's first day of college in September 2007 to tell her that police had exhumed her father's body and discovered that he had not died of a heart attack -- he had been murdered.

"I started crying," she recalled. "I got upset. Why would they dig up Daddy? He was resting peacefully. I thought it was inhumane, and I didn't like it whatsoever."