April 21, 2009 -- Earlier this year, the dramatic conclusion to a mystery that captivated an entire community played out in an upstate New York courtroom. Mother of two, Stacey Castor was charged with the murder of her husband and attempted murder of her 20-year-old daughter.
The bizarre story began four years earlier, in August 2005, when Stacey Castor was at work waiting for her husband, David, to arrive. Stacey Castor, now 41, worked as an office manager at her husband's business, Liverpool Heating and Air Conditioning.
According to Castor, the couple, from Clay, N.Y., had had a fight the previous weekend, but she said she was still surprised that her husband was so late getting to work. She said she called him at home and on his cell phone several times but failed to reach him. Finally, around 2 p.m., she said she became really worried and called the police to report her concerns.
"My husband has locked himself in our bedroom for the last day," she said, asking for police to meet her at their residence. When police arrived, Castor was waiting in the front yard. Sgt. Robert Willoughby of the Onondaga County Sheriff's Department recalled that she'd mentioned that David had been depressed and that she was worried about the gun he kept in the room.
Armed with that information, the sergeant made his way inside the home and knocked on the bedroom door. He could hear the television and "banged on the door" but didn't "get any response."
Willoughby tried unsuccessfully to look through the bedroom window but ultimately forced his way in.
"I kicked the door in," he said. "David was lying naked across the bed."
Next to him on the nightstand the police found cranberry juice, apricot brandy and a couple of glasses. According to Willoughby, "one of the glasses is half full of a bright green liquid" and lying on the floor next to the bed was an antifreeze container.
Willoughby called for paramedics, but by the time they arrived, it was too late. David Castor, 48, was dead.
"[Stacey Castor] asked me if he's OK," Willoughby recalled. "All I said was, 'No, he's not.'"
Castor became hysterical, he recalled, screaming, "He's not dead, he's not dead." Her friend Lynn Pulaski arrived and found her inconsolable and in shock.
Married for two years, Stacey Castor, by all accounts, had found her prince charming in David, a tall handsome man who owned his own business and loved the outdoors. Pulaski said Castor's husband made his wife feel safe and secure and doted on her right from the start, buying her dresses and taking her out for fancy dinners.
"Stacey was loved. She was treated like a lady," said longtime friend Dani Colman.
David Castor's Bizarre Death
Though things appeared to be perfect between the couple, Stacey Castor's two teenage daughters from her first marriage, Ashley and Bree Wallace, had a harder time connecting with their stepfather. According to Stacey Castor's mother, Judie Eaton, their relationship was strained.
David Castor was "difficult with the kids," she said. "He expected them to do everything he said without question. And them being my kids, they questioned everything and that created a lot of problems."
Dani Colman remembered that David used to call 17-year-old Ashley, the older daughter, "selfish and disrespectful." Ashley Wallace said her stepfather claimed "he didn't want to be our father, but then he acted in ways, he was trying to be."
Their hostile relationship, including a fight the weekend David Castor died, was a source of constant conflict in the house.
He was planning a vacation for the couple's wedding anniversary and wanted to be alone with his wife, but she refused to leave her younger daughter, Bree, 15 years old at the time, home. A heated argument ensued, and in the two years of their marriage, Stacey told ABC News that she had never seen her husband so angry.
Worried for her friend, Colman invited Stacey Castor to stay with her. Castor claimed she'd stayed on her own couch that night, but throughout the rest of the weekend kept her distance, getting out of the house as often as she could. She blamed her husband's belligerence on the alcohol he was consuming. She said she thought he was drunk when he fell and couldn't get up on his own. She grew annoyed when he locked her out of their bedroom but told friends she heard him snoring.
"She said she'd put her ear up to the door. She said she heard him snoring," Colman said. "You know, he snored like a Mack truck. So she knew he was in there sleeping."
But David Castor wasn't sleeping; he was slowly dying. When Detective Dominick Spinelli from the Onondaga Sheriff's Department walked onto the scene, he thought he knew why.
"One of the glasses was half full of antifreeze," Spinelli told ABC News' David Muir. "So it's thought, he must have gotten in some kind of argument and through some kind of depression, may have just committed suicide."
Castor explained to Spinelli that she thought the recent death of his father plus the rising stress of the business may have led her husband to take his own life.
Stacey Castor's Story: 'Something Strange'
Detectives searched and collected items from around the house, including the drinking glasses and various bottles from the bedroom and a turkey baster found lying in the garbage can in the kitchen. When Willoughby took a closer look, he noticed the cooking utensil looked brand new but smelled of alcohol and had a few drops of liquid in it.
"I found that very odd," he said. "He had no food around. No dirty dishes. No indication that anybody had been cooking or baking. I know he's been drinking. I know alcohol's involved. I know antifreeze was involved."
At the morgue, Chief Deputy Medical Examiner Robert Stoppacher conducted an autopsy. He found "there were crystals and the presence of those crystals in the kidney confirmed that he'd died of ethylene glycol toxicity."
In other words, David Castor died from anti-freeze poisoning. Virtually untraceable, toxicologists said the sweet-tasting liquid causes the organs to shut down, even after ingesting a small amount. It is both a slow and excrutiating way to die. Based on what he found in the report, the coroner concluded Castor had committed suicide.
"Why would he kill himself?" Ashley Wallace wondered. "I didn't know he was hurting like that. I was crushed."
His sister, Linda Horzempa, remembered the overwhelming disbelief she felt seeing her brother in his casket. "Why are you lying here? What happened?" she recalled asking.
Castor's first wife, Janice Poissaint, was convinced her ex-husband and the father of her only child, David Jr., cared about his life too much to end it. "He would never commit suicide," she said. "Never. He loved life."
Despite the medical examiner's findings, Spinelli, a street smart transplant from New York City, quietly refused to close the case.
"A sixth sense is something you develop throughout your career," he said. "It tells you something isn't right."
Weeks earlier, during their routine interview with Stacey Castor, she had mentioned that her husband may have chosen antifreeze after watching a documentary on Julia Lynn Turner, a woman in Georgia who was convicted of killing her husband and boyfriend with the toxic liquid. There was "something strange about it," and Spinelli couldn't let it go.
Investigation Builds in Castor Case
Further investigation into Stacey's phone records revealed that she'd only made one call to her husband the day he died.
Police also said that forensic tests on that seized glass, half full of antifreeze, determined that the fingerprints on it belonged to Stacey, not David, and the antifreeze container found on the floor had no prints on it at all.
"If David Castor poured a glass of antifreeze, then why isn't there one fingerprint on that container?" Spinelli said.
And that seemingly new turkey baster found in the garbage can had no prints on it either, but it did have David Castor's DNA on the tip.
Investigators said that Castor's death was no longer a suicide. It was a homicide. District Attorney William Fitzpatrick found Castor's decision to torture himself slowly with antifreeze using a turkey baster one drop at a time unbelievable.
"Suicide by turkey baster is not something I've even heard of in my career," he told ABC News.
As summer turned to fall, the quiet investigation into who could have killed David Castor began as his wife buried her second husband in a small cemetery tucked away in rural upstate New York, right next to her first husband, Michael Wallace. Wallace was 38 when he died, and police began to wonder if his untimely death was a coincidence or a pattern.
Over the next two years, investigators built a case against Stacey Castor, and in September 2007, she was arrested after what they believe was a desperate attempt to throw cops off her trail. She was ultimately convicted of second degree murder in David Castor's death and was also convicted of the attempted murder of her daughter Ashley.
"20/20" was granted full access to all sides of this curious investigation and trial. Stacey Castor talked about the trial and her conviction for the first time with ABC News' David Muir, who also sat down with the lawyers, detectives, doctors, family and friends who spent a decade watching this mystery unravel.
Go to the "20/20" page at ABCNews.com all week for more on this story and watch the two-hour special Friday on "20/20" at 9. p.m. ET.