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.
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.