Both Leopold and Loeb were transferred from Cook County jail to Joliet Penitentiary on 11 September 1924. Authorities initially separated them, by transferring Leopold to Statesville Prison, but they were eventually reunited at Joliet in 1931. Leopold continued his language studies, and the pair devised a plan to open a school for prisoners in 1932, which would ensure that they were kept together thereafter.
On 28 January 1936, Loeb’s cellmate, James Day, viciously attacked Loeb in the shower block, slashing him 58 times with a straight razor. He claimed that Loeb had made sexual advances to him, and was cleared of murder in the subsequent enquiry. Faithful to the end, Leopold was allowed to attend to Loeb immediately after his death, and spent considerable time washing the blood from his dead friend’s body. When his body was taken away Leopold said: “I felt like half of me was dead.”
Devastated by the death, Leopold continued his studies, and then began to make attempts to cultivate the press, in order to rehabilitate his image, playing on the hypnotic hold that Loeb had exercised over him, with a view to securing parole. His plea for parole in 1953 was unsuccessful, but he persevered and was finally released in March 1958. He fled to Puerto Rico, to avoid the press, where he taught mathematics at the University of Puerto Rico, and also published an ornithological book.
In 1961, he married a widowed American social worker named Trudi de Queveda, although a framed picture of Loeb always retained pride of place in their home. The rare interviews that he granted made it clear that his friend retained a profound influence over his life, even from beyond the grave.
On 30 August 1971, Leopold died of a diabetes-related heart attack, at home in Puerto Rico.