In France, it’s known as the "House of Terror": an elegant home in the city of Nantes where a woman and her four children were found buried in April 2011.

It’s a terrible crime that has obsessed the French for nine years. But now that it’s been featured in Netflix’s Unsolved Mysteries, there’s hope that the person responsible for the killings could finally be found and brought to justice. 

The house belonged to Count Xavier Dupont de Ligonnes, a businessman who lived there with his wife Agnes, a teaching assistant, and their children Arthur, Thomas, Anne and Benoit. The family seemed like they had it all. 

Listen to Mamamia's True Crime Conversations, which features interviews with experts on the world's most fascinating, terrifying and mysterious crimes. Post continues below. 

They were good-looking (Anne was a part-time model) and clever. But Xavier was hiding something – or perhaps several things. Financially, he was in major trouble. It’s also alleged that he had a mistress in Paris. 

French media have published an email he supposedly sent to his mistress, where he said he was "ruined, at rock bottom" and lying awake with "morbid ideas". 

"Most of the time I am not in a dream but in a nightmare and I can't escape except, of course, by doing something radical and final," the email read.

Xavier’s father died in January 2011, with barely any money to his name. Among the possessions that Xavier inherited from him was a rifle. Soon afterwards, he got a gun licence and bought a silencer. 

In early April, Xavier told his children’s school that the family was moving to Australia. The school that Agnes worked for was told the same thing. 

Thomas, who was living at a university hall of residence, received a call from his father telling him to come home because his mother had been in a serious bicycle accident. Neighbours heard howling from the family’s Labradors, Jules and Leon, which lasted two nights and then stopped. 

In mid-April, the families and friends of Xavier and Agnes received strange letters, purportedly from the couple. 

The letters claimed that Xavier was a spy for the US drug squad and he’d been transferred to the US to infiltrate an international drug ring. 

"Keep it secret!" the letters urged. 

Watch the trailer for Netflix's Unsolved Mysteries below. Post continues after video.

Agnes’s family found the letters suspicious and informed the authorities. Police checked the house and found nothing, but the family kept urging them to go back. It was only on the police’s sixth check that an officer discovered a leg buried behind the house, under the patio. 

That led to the discovery of the bodies of Agnes, Arthur, Thomas, Anne and Benoit, and their dogs. The bodies were wrapped in blankets and duvets, and each had been buried with a candle, cross or other religious icon. Each had been shot twice in the head. The four children had been drugged with sleeping pills before being killed.

There was no sign of blood anywhere in the house, and no fingerprints or DNA on the bodies. But the police immediately suspected Xavier of the murders. 

They managed to trace his movements, through security cameras and his credit card. He’d driven to the south of France and then, after checking into a cheap hotel in Roquebrune-sur-Argens, he was seen walking into the woods, holding a bag that appeared to contain a rifle. 

A massive search of the area was carried out, as it was thought he had died by suicide, but no body was found. 

Is it possible that Xavier wanted everyone to think he took his own life so that he could escape and start a new life? A lot of people think so. 

Xavier’s friend Bruno de Stabenrath told Unsolved Mysteries that he believed Xavier planned the whole thing to make it look that way. 

"Xavier escaped," he said.

The police put out an international warrant for Xavier’s arrest in 2011. Over the years, there have been some promising leads but none have resulted in Xavier being found. 

In 2015, a French journalist received a photo of two of Xavier’s children. Written on the back were the words "I am still alive from then until this hour". The photo was tested for fingerprints and DNA but nothing came of it.  

In 2018, police raided a monastery near Roquebrune-sur-Argens after reports Xavier had been spotted living among the monks. They struggled to get answers from the monks, as many of them had taken a vow of silence, but eventually realised the man in question was just a lookalike. 

In 2019, a man was arrested at Glasgow airport, with police claiming fingerprints showed he was Xavier. Although he didn’t look anything like the French count, it was suggested he might have had plastic surgery. 

However, further fingerprinting and DNA testing showed the man was not Xavier, but a much older person of Portuguese origin called Guy Joao. 

Now, with the case having gone to air on Unsolved Mysteries, old theories are being rehashed and new ones put forward. 

People are questioning how Xavier, who had a bad back, could have buried the bodies under the patio himself. Did he have an accomplice?

Others are wondering if some of Xavier’s extended family could somehow be involved, with Xavier possibly hiding on a secluded property somewhere. His ancestors had owned a castle in central France. 

But the most intriguing piece of information comes from Unsolved Mysteries executive producer Terry Dunn Meurer. She told Variety that the "most interesting tip" they got for any of the episodes this season was for Xavier.

"Somebody was actually in Chicago, I think they were on Lake Shore Drive, and they heard this guy talking French and they looked at him and they had just seen the episode," she said. "They sent us a photo, and it really did look like Xavier. It was striking. So we sent that tip on. But again, this is just a stranger – we don’t have a name, we don’t have anything specific."

Meurer says she’s really hoping that because of Netflix’s global reach, Xavier can be found. 

"If he’s alive," she adds. "That’s the mystery."

 Feature Image: Netflix.