Joseph Roland Ernst was born on February 17, 1937, in Camden, New Jersey. By the age of 19, he had been convicted of motor vehicle theft in 1956 and was on parole at the time of the murder. Details about his early life are limited, but his criminal activities suggest a troubled background.

On March 14, 1959, 22-year-old Joseph Ernst visited the home of Lawrence and Theresa Linden in Camden, where his 17-year-old ex-girlfriend, Joan Connor, was babysitting their children. After an argument, Ernst shot Connor multiple times, resulting in her death. He was arrested the same day and charged with first-degree murder.

Ernst was convicted on June 24, 1959, and sentenced to death. He appealed his conviction, but the New Jersey Supreme Court denied his petition for a writ of habeas corpus in February 1962. His execution was carried out on July 31, 1962, at Trenton State Prison. Ernst was the second-to-last person executed in New Jersey and the most recent executed against his will.