Lester Harrison was born on June 7, 1922, in Mississippi. Details about his early life are scarce, but he began exhibiting signs of mental illness in the late 1930s, coinciding with his involvement in minor criminal activities. In 1945, at the age of 23, Harrison was arrested and subsequently convicted on robbery charges, receiving a sentence of five to ten years in prison. He was incarcerated at the Southern Illinois Penitentiary in Chester (now known as the Menard Correctional Center). While serving his sentence, Harrison committed his first known murder on August 10, 1951, by fatally assaulting fellow inmate Norman E. Kimme with an iron rod. Harrison admitted to the killing but was declared insane and committed to the prison's psychiatric facility. He was later deemed "cured" and released back into society.

Following his release, Harrison's criminal activities escalated. Between the late 1950s and early 1970s, he amassed eight additional arrests for offenses including theft, attempted armed robbery, unlawful possession of a weapon, assault causing bodily harm, and public indecency. He served short prison sentences on four occasions, paid fines in two instances, and was twice committed to psychiatric wards after being found unfit for trial. During this period, Harrison subsisted on disability checks, consumed alcohol heavily, and developed an intense interest in pornography. He frequently visited Chicago's Grant Park to engage with various women.

On July 19, 1970, 46-year-old Agnes Lehmann, a homeless woman, was found raped and beaten to death in Chicago's Grant Park. That same night, 31-year-old Wilbur McDonald was found beaten unconscious nearby. McDonald was arrested and convicted for Lehmann's murder based on circumstantial evidence, receiving a 150-year sentence.

On September 5, 1972, 24-year-old English architect Judith Bettelley was found murdered and raped in the park. Shortly after, Harrison was arrested for assaulting a woman named Cozetta Gladys with a concrete brick but was released after posting bail. In July 1973, Irene Koutros was raped and stabbed to death, followed by 24-year-old Lee Alexis Wilson, an art student, who was killed under similar circumstances on August 3.

On August 13, 1973, Harrison attacked 28-year-old Judith Elaine Ott in a public restroom in Grant Park. Ott resisted and screamed, prompting Harrison to stab her multiple times, resulting in her death. Her husband, David Ott, chased and apprehended Harrison, leading to his final arrest.

During the investigation, Harrison admitted to four of the murders. However, he was again found not guilty by reason of insanity and committed to a mental health facility. He remained there until his death, which occurred sometime after August 1986.