His wife, Agnès Dupont de Ligonnès, and their four children, Arthur, Thomas, Anne and Benoît along with the family's two dogs, were killed on an undetermined day in early April 2011.

The exact nature of the events has never been determined, but Xavier is the subject of an international arrest warrant and is considered the prime suspect in the murders.

[8] In 2004, writing on the French online medical chat forum Doctissimo,[9][10] Agnès described the difficulties she and her husband were having and stated he had commented to her that a group death as a family would not be a catastrophe.

[11] At the time of the murders, Xavier and Agnès lived at 55 Boulevard Robert Schuman in Nantes, Loire-Atlantique,[12][13][14] in a modest house in the western suburbs of the city.

He lived in the Saint-Aubin hall of residence and was described as an "ordinary boy who was often accompanied by his family to drop him off and pick him up",[18] while several of his classmates remember him as "very discreet".

She was in the 11th grade following an academic curriculum in Science, and was described by her friends and relatives as a girl who shared her mother's religious beliefs and was considerate and approachable.

[62] According to an AFP press release in Le Monde, "administrators of a Catholic website, classified as fundamentalist by the episcopacy, confirmed that Xavier Dupont de Ligonnès was a member of their forum, where in 2010 he asked about the meaning of "sacrifice" and he recently became "aggressive".

Xavier Dupont de Ligonnès created Netsurf Concept LLC, a company that was recorded on the commercial register in Florida, United States.

[68] Prosecutor Brigitte Lamy has not reconsidered Xavier Dupont de Ligonnès's status as a suspect and leans towards the belief that he committed suicide.

[73] The prosecutor in Draguignan, Danielle Drouy-Ayral, stated "at this moment in time, it is not the body of Xavier Dupont de Ligonnès", without providing any more details to explain this declaration.

[74] On the evening of Tuesday 28 April 2015, a walker discovered bones in a forest in Bagnols-en-Forêt, near Fréjus on the south coast of France, close to where Xavier Dupont de Ligonnès was last seen.

[75] The police made a link with Xavier's disappearance and analysed what appeared to be a survival camp where other objects were discovered, including an empty wallet, a lighter, a pair of glasses, a sleeping bag, a magazine and a bill dating from 2011.

However, as far as the police are aware, Xavier Dupont de Ligonnès did not have a medical device in his forearm, even though it is not impossible that he may have been operated on after his disappearance.

On 1 May 2015, the RTL.fr website reported that "DNA obtained from the personal effects around the body discovered on the evening of 28 April in Bagnols-en-Forêt is not that of Xavier Dupont de Ligonnès, but that of another man whose identity is currently unknown.

The picture shows two of the Dupont de Ligonnès children – Arthur, the oldest and Benoît, the youngest – sitting at a kitchen table.

[78] On 9 January 2018, police raided the Saint-Desert monastery in Roquebrune-sur-Argens, the village where Xavier Dupont de Ligonnès was last seen, after several worshippers claimed that they had seen him there.

However, after a two-and-a-half-hour search, they determined that the reports were a case of mistaken identity, and the person believed to be Dupont de Ligonnès was a monk who bore a resemblance to him.

On 12 October, following more thorough fingerprinting and a DNA test, it was announced that the arrested man was not Xavier Dupont de Ligonnès, but a 69-year-old Portuguese-born French national visiting his Scottish wife in Dunoon.

"[88]Christine de Verdun also cites on her blog the difficulties faced by a person burying five people underneath the garden patio.

Finally, it is surmised that due to the low headroom, the perpetrator would likely have both banged their head and rubbed their hair on the ceiling repeatedly, but no human skin cells, blood, or DNA were found there.

Most notably, in 2016, someone matching his physical description was caught on CCTV in a casino in Néris-les-Bains, and the police subsequently concentrated their search on the area.

[91] The plot revolves around a man, Thomas Kertez (played by Kad Merad), his wife Alice (Laurence Arné) and their eight-year-old son Romain (Gaspard Pasquet), an ordinary family whose lives are turned upside down when the police suspect that Thomas is living under a false identity and is actually Antoine Durieux-Jelosse, a man suspected of murdering his family 15 years earlier before going on the run and not being seen since.

[93] In 2020, Netflix resurrected the Unsolved Mysteries series and the Dupont de Ligonnès murders were investigated in the third episode, "House of Terror".