In April 2011, police dug up the back garden of the Dupont de Ligonnès family and made a shocking discovery. Agnès Dupont de Ligonnès and her four children had been shot and their bodies buried under the back patio of their own home, and their father, Xavier Dupont de Ligonnès, had disappeared. 

Sources:

https://medium.com/the-mystery-box/unsolved-mysteries-where-is-count-xavier-dupont-de-ligonn%C3%A8s-f8b8bab85ebd

https://en.wikipedia.org/wiki/Dupont_de_Ligonn%C3%A8s_murders_and_disappearance

https://www.radiotimes.com/tv/documentaries/true-crime/xavier-dupont-de-ligonnes-unsolved-mysteries/

https://unsolvedmysteries.fandom.com/wiki/Xavier_Dupont_de_Ligonn%C3%A8s

https://www.strangeoutdoors.com/strange-indoors/xavier-dupont-de-ligonnes

https://www.esquire.com/entertainment/tv/a33249023/xavier-dupont-de-ligonnes-netflix-unsolved-mysteries-sightings-today/

https://www.france24.com/en/20150724-france-photo-man-suspected-killing-family-nantes-murder-dupont-de-ligonnes

https://www.grunge.com/224521/the-untold-truth-of-the-dupont-de-ligonnes-murders/