Marybeth Davis, born around 1952, was a registered nurse residing in Lewisburg, West Virginia. She was married to Gary Davis, with whom she had two children: Seth and Tegan. As a healthcare professional, Marybeth was entrusted with the well-being of her patients and was expected to possess a deep understanding of medical ethics and patient care.​

On September 30, 1981, Marybeth's 10-week-old son, Seth, was hospitalized with severe seizures and hypoglycemia. Medical examinations revealed an abnormally high level of insulin in his system, suggesting an exogenous source. The damage to Seth's brain was extensive, leading to permanent disability. He remained institutionalized until his death on October 10, 2002, at the age of 21. ​

Several months later, on March 11, 1982, Marybeth's 3-year-old daughter, Tegan, died from a caffeine overdose. An autopsy uncovered lethal amounts of caffeine in her system, with numerous caffeine capsules found in her digestive tract. The medical examiner concluded that the manner of death was homicide. ​

Despite the suspicious nature of both incidents, it wasn't until 1996 that Marybeth was indicted for the murder of Tegan and the attempted poisoning of Seth. During her 1997 trial, prosecutors suggested that Marybeth suffered from Münchausen syndrome by proxy, a disorder wherein a caregiver induces illness in others to gain attention. The defense argued that the children had underlying medical conditions, including claims that Tegan had Reye's syndrome and Seth had a genetic disorder. Nonetheless, Marybeth was convicted and sentenced to life imprisonment without the possibility of parole. ​

In 2007, after maintaining her innocence for years, Marybeth accepted a plea deal and confessed to the crimes, leading to her release from prison.