Diane Pfister was born in 1949 in Wisconsin, USA. In 1979, at the age of 31, she met 25-year-old widower Ruben Borchardt, who had two young children from his late wife, Susan. Diane and Ruben married shortly after meeting and had a daughter named Regan. Diane worked as a teacher's aide at the local high school, where she was well-liked by both students and staff, earning the affectionate nickname "Mrs. B." Despite her outwardly friendly demeanor, Diane was known to be controlling and jealous, particularly towards Ruben's late wife, Susan. She attempted to erase all traces of Susan from their home and insisted that Ruben's children refer to her as their mother. Over time, Diane's behavior became increasingly erratic and abusive, leading to a tumultuous marriage.​

By 1993, Ruben Borchardt had become involved in an extramarital affair and decided to divorce Diane. The divorce proceedings were contentious, with Diane seeking sole custody of their children and a significant portion of their assets. However, the court granted Ruben custody of the children and ownership of the family home, ordering Diane to vacate the premises by April 15, 1994. Feeling betrayed and enraged by the court's decision, Diane began plotting Ruben's murder. 

She manipulated three of her students—Douglas Vest Jr. (17), Joshua Yanke (16), and Michael Maldonado (15)—by portraying herself as an abused and victimized wife. Diane promised them money, cars, jewelry, and a share of Ruben's life insurance payout in exchange for carrying out the murder.

On April 3, 1994, while Diane was conveniently out of town, the three teenagers entered the Borchardt home and shot Ruben as he was ascending the basement stairs. Ruben's son, Chuck, discovered his father bleeding and called for help. Despite being rushed to the hospital, Ruben succumbed to his injuries. The investigation quickly focused on Diane due to the acrimonious divorce and her suspicious behavior. 

In August 1995, Diane Borchardt was convicted of first-degree intentional homicide and sentenced to life in prison, with eligibility for parole after 40 years. The three teenagers involved in the murder were also convicted and received varying sentences for their roles in the crime.​