William Kessler Lilly was born on March 22, 1962, in Springfield, Ohio. He was the oldest of two boys; he had one younger brother. During his childhood, he showed signs of hostility toward women, as noted by children's services. When William was nine years old, his parents divorced. After the divorce, he and his brother moved in with their father and stepmother. They later reported that they faced both physical and mental abuse from their stepmother.

William Kessler Sapp was involved in a series of murders in the early 1990s. On August 23, 1992, the bodies of two young girls, 12-year-old Phree Marrow and 11-year-old Martha Leach, were found near a pond. The girls had been killed the day before while returning home from a bakery. In July 1995, another victim, 30-year-old Belinda Fay Anderson, was discovered under a garage in Springfield. Anderson had been missing since September 1993.

Sapp was arrested on February 27, 1996, for the attempted murder of Una Timmons. During his trial, he pleaded not guilty by reason of insanity. Investigators began looking into his past and questioned him about other potential crimes. While in custody, Sapp provided information about some murders, but he also tried to shift blame to another man.

DNA evidence linked Sapp to the murders of Phree Marrow and Martha Leach. In an interview with detectives, Sapp confessed to killing them and also admitted to the murder of Belinda Anderson. At that time, two other men were already in prison for the deaths of Marrow and Leach. Investigators confirmed that Sapp was actually the ringleader.

On October 13, 1999, Sapp was convicted of the murders of the three victims. Shortly after, he was sentenced to death. Following his conviction, Sapp signed over his parental rights of his children to his wife, and she later gave up custody as well. The children became wards of the state until they were placed with a local family in 2001.