Nathan Leopold was born in 1904 and met Richard Loeb at an elite prep school in Chicago. Obsessed with committing "the perfect crime," in 1924 they killed a 14-year-old boy and contacted his family for ransom. The police found the body, and Leopold and Loeb—defended by Clarence Darrow—were convicted of murder, but avoided the death penalty. Leopold died in Puerto Rico in 1971.

Murderer Nathan Freudenthal Leopold Jr. was born on November 19, 1904, in Chicago, Illinois. Leopold was the son of a wealthy family of immigrant German Jews who had made a freight and transport-related fortune since their arrival in the United States. Reportedly a child prodigy with an IQ of 210, Leopold spoke his first words at 4 months old and amazed a succession of nannies and governesses with his intellectual precocity.

Leopold's intelligence set him apart from his contemporaries, and the boy had difficulty making friends when he started school. This was a trait that continued throughout his education, and was made more difficult by his own superior attitude, in relation to both his family’s wealth and his own intelligence. When the family moved to the exclusive Chicago neighborhood of Kenwood, he was transferred to the private Harvard School, and his educational development was even more rapid. It was at this time that he met Richard Loeb, although it wasn't until he entered the University of Chicago, as a freshman in September 1920, that they became what he referred to as "firm friends."

Leopold and Loeb were an excellent match psychologically: the brilliant but socially inept Leopold was enthralled by the handsome and vivacious Loeb; and Loeb found an excellent alter ego for his fantasy world in which he was supreme. By the summer of 1921 they were inseparable, and it is likely that they began a sexual relationship. Leopold graduated with honors in March 1923; Loeb barely graduated from the University of Michigan in June 1923.

Both men returned to Chicago, where they were inseparable. Both pursued post-graduate studies at the University of Chicago while living at home. Loeb continued to embroil Leopold in a number of criminal pursuits, using the promise of sexual favors as an enticement, and became increasingly obsessed with the development and commission of the perfect crime.

On May 21, 1924, Loeb and Leopold put their plan into action, collecting a rental car, obscuring its number plates and then driving to their old alma mater, the Harvard School, in search of a convenient victim. They settled on 14-year-old Bobby Franks, a neighbor of the Loebs. Lured into the car, Franks was hit over the head with a chisel by Loeb and gagged before being hidden under some blankets on the back seat of the car. After depositing Franks' body in a culvert at nearby Wolf Lake, they delivered the ransom note to the boy's father, Jacob Franks.

Unbeknownst to Leopold and Loeb, Jacob Franks had contacted the police, and Bobby Franks' body was found and identified before the ransom was delivered.

Leopold and Loeb were interrogated by police and eventually Loeb admitted the murder, claiming that Leopold had been the driving force behind the plan and that he had struck the fatal blow on Franks. Leopold claimed the opposite was true. The families hired Clarence Darrow, the country's foremost criminal defense lawyer, to represent the pair at trial. On September 24, 1924 Leopold and Loeb each received a life sentence for the murder, rather than the death penalty, and an additional 99 years each for the kidnapping.

While serving his sentence in Joliet Penitentiary on September 11, 1924, Loeb was viciously attacked and killed by his cellmate, James Day, who claimed Loeb had made sexual advances to him. Leopold was eventually granted parole in March 1958. He fled to Puerto Rico, 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. On August 30, 1971, Leopold died of a diabetes-related heart attack.