The Dupont de Ligonnès murder mystery is perhaps the most unsettling case featured in the reboot. On April 21, 2011, the police made a disturbing discovery underneath the terrace of the Dupont de Ligonnès home in Nantes, France: the dead bodies of Agnès Dupont de Ligonnès, her four children, and their two family dogs. The children had been given sleeping pills, and each person was shot several times in the head. The person missing from this picture was Xavier, the husband and father.
While Xavier Dupont de Ligonnès left no biological evidence, it's likely he committed the tragic killings. He had sent letters to loved ones saying that he was a secret agent moving to America with his family. Shortly before the massacre, he had also inherited a .22 rifle from his father and bought a silencer. Weeks before the bodies were discovered, Dupont de Ligonnès travelled throughout southern France. He was last seen in Roquebrune-sur-Argens, where he abandoned his car at a hotel.
While the police believe he committed suicide in the backcountry, a friend and journalist featured episode three believe that he may have left for Latin America, as his English and Spanish are good. It's been an unsettling decade for the case. In 2015, someone sent a Nantes journalist a photograph of two Dupont de Ligonnès children, writing "I am still alive" on the back and signing as Xavier. Over the years, bodies have been found and lookalikes have been spotted, but none of them were Xavier.