John Errol Ferguson was born on February 27, 1948, in Miami, Florida. He was the fourth of eight children. His father died when he was 13, leaving his mother to raise the family alone. From a young age, Ferguson exhibited behavioral issues and had multiple encounters with law enforcement. At 13, he was caught driving a stolen car.

Ferguson dropped out of school after repeating the ninth grade three times. In 1969, he attempted to murder a police officer during a traffic stop, leading to his arrest. Over the years, he was diagnosed with paranoid schizophrenia and deemed dangerous by multiple psychiatrists. Despite these evaluations, he was released from mental health facilities multiple times.

In 1975, a court-appointed psychiatrist described him as "dangerous to himself and others" and "homicidal." Another psychiatrist noted his potential for recovery was minimal. 

On October 30, 1974, James Ward, a 40-year-old escapee from a mental hospital, was found murdered by a shotgun blast in Collier County, Florida. Just two days later, on November 1, Joseph Walters was discovered dead near railroad tracks in Miami, having suffered a shotgun blast and multiple handgun wounds. These cases remained unsolved until February 1977, when Edward Eugene Oliver, already convicted for Ward's murder, confessed to both killings. Oliver implicated Ferguson as the shooter in both incidents, stating that the victims were part of a gang involved in robberies and that disputes over stolen merchandise led to their deaths. Despite Oliver's confession and passing a polygraph test, Ferguson was never prosecuted for these 1974 murders.

On July 27, 1977, Ferguson, along with accomplices Marvin Francois and Beauford White, orchestrated a home invasion in Carol City, Florida. Posing as a utility worker, Ferguson gained entry to the home of Margaret Wooden. Over the next several hours, they bound and blindfolded eight individuals who arrived at the house. The victims were then executed with gunshots to the head; six died, and two survived to testify against the perpetrators. This incident was the largest mass murder in Miami-Dade County at the time.

On January 8, 1978, Ferguson committed another heinous act by murdering two teenagers, Belinda Worley and Brian Glenfeldt, in Hialeah, Florida. The couple was last seen leaving a Youth for Christ meeting. The next morning, their bodies were discovered in a wooded area; Brian had been shot multiple times, and Belinda had been raped and shot in the back of the head. Jewelry was missing from Belinda's body, and Brian's wallet was found empty, indicating robbery as a motive.

Ferguson was arrested on April 5, 1978, and subsequently convicted for the Carol City and Hialeah murders. During his trials, debates over his mental competency arose, with defense attorneys arguing that he suffered from paranoid schizophrenia. Despite these claims, courts found him competent to stand trial, and he was sentenced to death. Ferguson spent over three decades on death row, during which he continued to exhibit signs of mental illness, including delusions of being the "Prince of God."

After numerous appeals focusing on his mental health, Ferguson was executed by lethal injection on August 5, 2013. His case remains a controversial example of the intersection between mental illness and the criminal justice system.