THE reboot of the classic true-crime show Unsolved Mysteries has taken the world by storm.
The third episode of the Netflix show tells the story of the DuPont de Ligonnès murders and the theories behind Xavier's disappearance.
What are the details of the case?
On April 21, 2011, investigators discovered the remains of five humans and two labradors buried beneath their terrace.
The bodies belonged to Agnes DuPont de Ligonnès and her four children: Arthur, Thomas, Anne, and Benoît.
The autopsy found that the children were given sleeping pills.
Each person was seemingly put to sleep, then shot at least twice in the head with bullets from a .22 rifle.
The theory is that 50-year-old Xavier DuPont De Ligonnès killed his wife and children.
What are the theories?
Although he is the primary suspect in the gruesome murders, Xavier DuPont de Ligonnès has never been found.
Xavier, who is the subject of an international arrest warrant, was last seen on CCTV in April 2011, near a budget hotel where he abandoned his car.
The whereabouts of Xavier have puzzled investigators for nearly a decade.
Xavier killed himself
Officially, investigators believe that Xavier killed himself.
He left the hotel, he went to the wilderness, full of caves and cliffs, and killed himself.
Police and sniffer dogs were dispatched to search the area, but there were no signs of Xavier.
Usually, the perpetrator of familicide would kill themselves at the crime scene, so it struck officers and journalists as bizarre that Xavier would do it elsewhere.
Xavier is on the run
Chillingly, there is a growing theory in the true crime community that Xavier is still alive and is on the run.
According to the Netflix show, he could have taken a cargo ship in Fos, headed on the highway towards Italy, or even boarded a train to Croatia.
There have been many reported sightings of him, but none of them have amounted to anything.
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In 2015, someone, signing as Dupont de Ligonnès, sent a Nantes journalist a picture of Dupont de Ligonnès' sons Arthur and Benoît.
On the back, there was a handwritten note that said, "I am still alive."
Where can I watch Unsolved Mysteries?
The first series of Unsolved Mysteries is available to binge on Netflix UK now.
The show, which dropped on Netflix on July 1, is a reboot of the 1987 show of the same name.
It is a 12-part series where each episode looks at a different unsolved mystery.
The first episode is title Mystery on the Rooftop, and looks at the 2006 death of Rey Riviera.