Two French judges arrived in Algeria on Sunday to investigate the unsolved murder of seven French monks in 1996. The Roman Catholic monks were kidnapped during the Algerian Civil War and held hostage for two months before their severed heads were discovered on the side of a road. Their bodies were never recovered.

The visit by the two magistrates — anti-terror judge Marc Trévidic and investigating judge Nathalie Poux — coincides with an autopsy that may help determine whether a radical Islamist group or the Algerian army should be held responsible for the killings.

The former French colony was in the midst of a decade-long civil war when the monks were abducted from the monastery of Notre-Dame de l'Atlas in Tibhirine, near the town of Médéa, 50 miles southwest of Algiers, on the night of March 27, 1996.

On May 21, 1996, the Armed Islamic Group (GIA), a militant group fighting the Algerian government, claimed responsibility for the killings, an explanation that was accepted and supported by Algerian authorities. However, over the past 10 years, witness statements and investigations by journalists from both sides of the Mediterranean have sparked different theories, prompting the case to be reopened. French courts had been asking for months for access to the remains of the monks.

According to sources at the French newspaper Le Figaro, the two judges spent Monday making arrangements for the rest of the week. Starting Tuesday, they will be traveling back and forth every day between Algiers and the monastery where the remains are buried, about 50 miles southwest of the capital.

Patrick Baudoin, a lawyer who represents the families of the dead monks, told VICE News that the autopsy was likely prompted by the presence of the French legal team. "What motivated this shift is without a doubt the fact that the Algerian authorities could no longer refuse an autopsy without raising strong suspicions," he said.

According to Baudoin, the purpose of the exhumation is twofold: Investigators will attempt to formally identity the bodies with DNA testing, and also determine the circumstances of their deaths.

"Did they have their throats slit before they were beheaded? Were they beheaded after their death, or before? They will also be looking for bullet impacts on the skulls," Baudoin said.

'The only thing I know for sure is that we cannot believe the official version given by the Algerian government.'

Why go looking for bullets in severed heads? On June 25, 2009, Trévidic, the visiting anti-terror judge, heard surprising testimony from a former member of the French military. The ex-soldier revealed that the monks may have been killed when Algerian soldiers opened fire on a suspected guerilla camp from a helicopter. Once on the ground, the soldiers allegedly discovered the monks among the dead, then beheaded them to disguise their mistake as a GIA execution.

Another hypothesis involves an operation conducted by the Algerian secret service. According to investigative journalist Jean-Baptiste Rivoire, an expert on the civil war in Algeria and the author of a book about the beheadings, the Algerian government directed the GIA to kidnap and murder the monks.

"My assumption is that, between 1994 and 1996, Djamel Zitouni, the main chief of the GIA, was manipulated," Rivoire said. "Manipulated by the military to help wage the war against Islamist insurgency. The GIA might have been used by authorities to eliminate the monks who were considered troublesome."

Rivoire interviewed several former Algerian secret agents living in exile who reportedly claimed that the monks were targeted because they cared for injured insurgents that showed up at the monastery. Rivoire suspects the Algerian government faked the kidnapping of the monks by the Islamists.

The monks were initially going to be sent back to France, Rivoire claims, but the plan went awry when the French secret service raised suspicions that the monks were actually in the hands of the Algerian government.

"In order to hush these rumors, the Algerian secret service would have been forced to eliminate the monks," Rivoire told VICE News.

Baudoin, the attorney representing the families of the monks, was less certain. "The only thing I know for sure is that we cannot believe the official version given by the Algerian government," he said.

Baudoin added: "I am inclined to think that the Algerian authorities are implicated in the abduction."

According to Baudoin, Algerian authorities had asked the monks to leave the country several times in the months leading up to their abduction. The attorney also said the Islamists had no motive for the kidnapping, noting that the monks had been caring for their wounded fighters.

To get a better picture of the monastery at the time of the incident, VICE News spoke to René Guitton, author of a 2011 book about the monks. Guitton had known some of the monks as a child, and, as an adult, launched his own investigation into their abduction.

"The monks had been in Tibhirine since 1948," Guitton said. "They were caught in the crossfire between the jihadists and the army. The presence of the monks irritated the jihadists, but not those operating in the region, who were familiar with them and knew their relationship with the people. At the same time, the Algerian authorities had asked the monks to return to France. The monks didn't want to, they wanted to partake in the suffering of their Algerian brothers."

Guitton told VICE News that he discovered key Algerian documents, including photographs of the seven severed heads at the time of their discovery by the national Algerian gendarmerie.

"I had the pictures assessed by forensic experts from several cities in France, who said that all the heads displayed signs of impact," Guitton said. "One of the heads is unrecognizable. The skulls will reveal what weapons were used, but not the hand that used them."

It remains to be seen whether the two French magistrates will be free to collaborate with the Algerian authorities, or if their investigation will be obstructed. The visit will unfold under the cloud of the beheading of French hostage Hervé Gourdel, who was killed in Algeria a few weeks ago by terrorists claiming links to the Islamic State.

"There is no doubt that Trévidic [the anti-terror judge] is an extremely competent, skilled and intelligent man," Baudoin told VICE News. "He could move the investigation forward by challenging certain witnesses, if he were authorized to hear these Algerian witnesses."

But Rivoire doubts the judge will have that kind of access.

"I am quite skeptical about the Algerians letting Marc Trévidic do his job," Rivoire said. "Algerian authorities have refused to let him interview the 20 or so witnesses he had planned to hear. Authorities also refused to let forensic testing be undertaken by French experts. Nor will Trévidic be allowed to sleep at Tibhirine. He will have to go back and forth every day."

Rivoire blames the lockdown on the fact that the Algerian secret service has been headed by the same person, general Mohamed Lamine Mediène, also known as "Toufik," since 1990.

"If Trévidic makes discoveries, it will pose a threat to the most powerful man in Algeria," Rivoire said. "People are terrified. Algeria is a country where you can be abducted in the middle of the night without there being any investigation. It makes the judges' work very complicated. There will be progress when Toufik Mediène retires."