An undated picture shows four-year-old Gregory Villemin. File photo: AFP

Gregory Villemin was four years old when he was murdered on an autumn day in 1984, his hands and feet tied when his body was found in a river in eastern France.

The case of "little Gregory", as it became known, has haunted the judiciary, media and the French public for four decades, with its resolution just as elusive today as it was on October 16, 1984, when he was found.

Investigators have amassed close to 18,000 reports bound in 42 volumes over the decades, and seven investigating judges have worked on the case, said Philippe Astruc, chief prosecutor in the eastern city of Dijon, where the investigation is still open.

At times, the probe's twists and turns seemed to come straight from a TV mystery - one suspect was murdered, an investigating magistrate died by suicide and charges were brought several times, only to be dropped.

"I don't know how we survived," Jean-Marie Villemin, Gregory's father, said about the past 40 years in a comic book published recently, one of many works dedicated to the Gregory mystery.

Gregory's parents mourn in front of his son's coffin during the funeral in Lepanges-sur-Vologne on October 20, 1984. Photo: AFP

'This is my revenge'

At first the investigation appeared to go quickly. A written note was sent to Jean-Marie Villemin saying: "This is my revenge, you sad fool".

Villemin, 26 at the time, and his wife Christine, 24, had been receiving anonymous, threatening letters and phone calls for years.

The murder investigation initially focused on the extended Villemin family. There was a media frenzy, with one journalist even hiding a microphone in the wardrobe of a family member in the hope of recording a confession.

Investigating magistrate Jean-Michel Lambert hoped the case would give him the break he hoped for in his first job in the judiciary.

In under three weeks the 32-year-old brought charges against Bernard Laroche, a cousin of Gregory's father, who was later released on bail.   

Jean-Marie Villemin holds a rifle during the reconstruction of the murder of his cousin Bernard Laroche, whom he suspected of being the murderer of his son Gregory. Photo: AFP

'Incompetent'

Gregory's father was convinced that Laroche was his son's murderer. In March 1985, weeks after Laroche's release, Villemin killed him with a rifle.

He was jailed for five years for the killing and did 34 months of jail time.

The investigation sensationally turned to Gregory's mother, who was charged with murder in 1985, but the charges were withdrawn because of errors committed by investigating magistrate Lambert.

"The work the judiciary did was pathetic," said Thierry Moser, a lawyer for the Villemins who has been involved in the case for 39 years. "The investigating magistrate was incompetent."

Lambert committed suicide in 2017.

Subsequent investigators failed to make a breakthrough.

In 2017, charges were laid against Gregory's great aunt and great uncle, Jacqueline and Marcel Jacob, as well as Murielle Bolle, an adolescent who had at one point given a witness statement against Laroche.

Within a year, all three cases were dropped on legal technicalities.

After decades of failure, there is now hope that modern DNA analysis and voice recognition software could help identify the man, or people, who harassed the Villemin family for years.

"I'm reasonably optimistic," Moser said.

A lawyer on the case, Francois Saint-Pierre, said it was still possible to save the investigation. "Today we're able to solve the mystery of the Pharaohs, so why not this one too?" he said.

But Etienne Sesmat, a former gendarmerie colonel who worked on the murder at the start, said that, crucially, police never found any case-specific DNA, typically contained in blood or sperm.

"All we have is contact DNA" that did not necessarily allow firm conclusions, he said.

Sesmat, who has published a book on the case, said that as far as he was concerned, it was "established" that the killer was Bernard Laroche, a view shared by the Villemin couple's lawyers.

Some lawyers have suggested that the case will never be solved, but Dijon chief prosecutor Astruc rejected that speculation.

"We must go on," he said. "We owe that much to this little boy and to his parents."

View of the Vologne River, where the body of Gregory Villemin was found on October 16. Photo: AFP