Mary Jane Fonder was born on July 5, 1942, in Philadelphia, Pennsylvania, to Edward and Alice Fonder. She grew up in West Philadelphia alongside her brother, Edward Fonder IV. From a young age, Mary Jane exhibited emotional difficulties, experiencing a "nervous breakdown" at the age of eight. At twelve, her family acquired a second home in Springfield Township, Bucks County, where she would later reside.​

Mary Jane attended John Bartram High School but faced academic challenges due to her emotional struggles. At sixteen, she attempted suicide by overdosing on chloral hydrate, leading to a month-long institutionalization. Following this, she left high school and found social interactions increasingly challenging.​

Throughout her early adulthood, Mary Jane held various jobs, including positions at a ceramics studio, department store, knitting factories, and as a punchcard operator at J. B. Lippincott & Co. publishing company. She began dating in her late thirties but never entered into a serious romantic relationship. In 1987, at 45, she returned to the family's Springfield home to care for her aging parents. Her mother, Alice, underwent leg amputation surgery in 1992 due to circulation issues but fell into a coma and passed away four months later.​

In the aftermath of her mother's death, Mary Jane's relationship with her father, Edward Fonder III, became strained. On August 26, 1993, Edward, then 80, disappeared from their Springfield Township home. Mary Jane claimed she heard the front door open that morning, assuming her father was retrieving the newspaper. After waking around 11:00 a.m., she realized he was missing and contacted the police. 

Despite searches by law enforcement and neighbors, Edward was never found. Authorities viewed Mary Jane as the prime suspect in his disappearance, noting inconsistencies in her statements and suspicious findings at their residence, including a bucket of pinkish water and a deceased dog in the freezer. However, due to insufficient evidence, no charges were filed. ​

On January 23, 2008, Rhonda Smith, a 42-year-old congregant, was shot twice in the head while working in the office of Trinity Evangelical Lutheran Church in Springfield Township. Mary Jane, then 65 and a longtime member of the church, became a suspect early in the investigation. The church's pastor informed police of Mary Jane's history of inappropriate behavior, including leaving lengthy voicemail messages and placing food in his kitchen without consent. 

Investigations revealed that Mary Jane had called the church on the day of the murder and learned that Rhonda would be alone in the office. After the shooting, Mary Jane attended a hair appointment, leaving her wig at the salon, which was later retrieved by police. A significant breakthrough occurred when fishermen discovered a .38 caliber revolver on the shore of Lake Nockamixon. Forensic tests confirmed it was the weapon used to kill Rhonda and was registered to Mary Jane. She was arrested on April 1, 2008, and charged with first-degree murder. ​

During her trial, prosecutors argued that Mary Jane was motivated by jealousy, believing Rhonda was receiving attention and support from the church community that she herself desired. On October 30, 2008, Mary Jane was found guilty of first-degree murder and possession of an instrument of crime. She was sentenced to life imprisonment without the possibility of parole. ​

Mary Jane Fonder died of cardiac arrest on June 4, 2018, at the State Correctional Institution in Muncy, Pennsylvania. Despite her death, the investigation into her father's disappearance continued, with authorities aiming to provide closure and a proper burial for Edward Fonder III. ​