Stacey Ruth Castor was born Stacey Daniels in Clay, New York, on July 24, 1967. She was the daughter of Jerry Daniels and Judie Eaton. Stacey had a relatively normal childhood growing up in a small town. She met her first husband, Michael Wallace, in 1985 when she was just 17 years old. The couple married and welcomed their first daughter, Ashley, in 1988. Three years later, in 1991, they had a second daughter, Bree.

Stacey worked at an ambulance dispatch company while Michael worked nights as a mechanic. The family struggled financially. Stacey later claimed that Michael had a closer bond with Bree, which caused her to form a strong friendship with Ashley to compensate. As time passed, the couple grew apart, and rumors of extramarital affairs began to surface within their marriage. In 2003, Stacey married David Castor, who owned an air conditioning installation and repair business. She became his office manager. 

In late 1999, Michael Wallace, Stacey Castor's first husband, began to feel very ill. He showed signs of being unsteady and swollen. Despite his family's concern, he did not seek medical help and died in early 2000. The doctors said he died from a heart attack. However, his sister doubted this and wanted an autopsy, but Castor refused.

In 2003, Castor remarried David Castor. In August 2005, she called the sheriff's office and reported that David had locked himself in their bedroom and had not been seen for a day. Police forced the door open and found David dead. Nearby was a glass with a bright green liquid and antifreeze. The coroner ruled it a suicide from antifreeze, but police later found Castor's fingerprints on the glass and a turkey baster with David's DNA. They suspected she had poisoned him.

Investigators monitored Castor's home and the graves of her husbands, who were buried next to each other, but she never visited. They exhumed Michael Wallace's body and discovered antifreeze poisoning, just like David.

In September 2007, with growing suspicion against her, Castor allegedly attempted to frame her daughter Ashley for the murders. On Ashley’s first day of college, police informed her about her father Wallace’s death being a poisoning. Ashley called her mother, who invited her over for drinks. The next day, Ashley was found unconscious in bed after drinking a substance her mother had made. A note next to her claimed she confessed to the murders, but Castor took the note and later gave it to paramedics.

Tests on Ashley revealed that she had taken painkillers that could have killed her if help had not been sought in time. When Ashley woke up, she told police she did not write the note and that she did not remember much before collapsing. The authorities collected evidence over two years and arrested Castor in 2007 for David's murder and for attempting to murder Ashley.

During the trial, which lasted four weeks, prosecutors claimed that the suicide note and the circumstances of David's death were suspicious. They pointed out that David's fingerprints were not found on the glass of antifreeze. Castor's lawyers tried to create doubt, suggesting Ashley could have been responsible for the murders due to jealousy. However, Ashley testified against her mother, asserting that she did not harm anyone.

On February 5, 2009, Castor was found guilty of second-degree murder for David’s death and attempted murder for trying to harm Ashley. She was sentenced to a total of 51 years in prison. The judge noted that he had never seen a parent try to frame their own child for such terrible acts.

After Castor's conviction, she was incarcerated at Bedford Hills Correctional Facility. On June 11, 2016, she was found dead in her cell. The cause was determined to be a heart attack, with no foul play involved.