Alain Gauthier, a retired French headmaster from Reims, is living out of a suitcase for the next five weeks. He is staying in a borrowed apartment in Paris while he and his Rwandan-born wife, Dafroza, attend the ground-breaking trial of an alleged participant in the 1994 Rwandan genocide.
The trial of the former Rwandan intelligence chief Pascal Simbikangwa, which opened on Tuesday, is the first trial on French soil of an alleged "génocidaire", as the suspects from Rwanda's armed Hutu majority are known in France.
It is largely because of 13 years of unrelenting effort by the couple that Mr Simbikangwa, a former army captain, is being brought to justice.
The former official was arrested in the French overseas territory of Mayotte in 2008 under a complaint filed by the victims' association founded in 2001 by Mr Gauthier and his wife, an ethnic Tutsi. Mr Gauthier says that French authorities, which were close allies of the Hutu-led government in 1994 and which have been accused of sheltering génocidaires, had no option but to arrest him. "He had been in prison for trafficking in forged documents. The magistrates realised he had an international warrant out, and our association had issued a complaint."
Mr Simbikangwa, a paraplegic since a 1986 road accident, faces charges of complicity in genocide and crimes against humanity, which he denies.
Mr Gauthier insists their campaign is not a personal search for revenge. Dafroza, 59, lost "at least" 80 members of her family, including her mother, in the 100 days of the pre-planned massacres sparked by the shooting down of the plane carrying the country's Hutu President, Juvénal Habyarimana. The 800,000 victims of the Hutu army and extremists were mainly Tutsis and moderate Hutus. When the couple visited Dafroza Gauthier's native Butare area in 1997 looking for her relatives, "we found nobody. The land was emptied and the property taken over".
Mr Gauthier points out that none of the 25 suspects living in France, who are sought by their Collectif des Parties Civiles pour le Rwanda (Collective of Rwanda Civil Plaintiffs) is linked to the murders of Dafroza's family. "We are working on behalf of all of the victims. In a way, the first trial is dedicated to them," he says.
Mr Gauthier met Dafroza when he was working in Rwanda as a young teacher. In 1973 she sought political asylum in Belgium and came across Mr Gauthier again in France. They married in 1977 and now have four children, aged between 25 and 33.
Mr Gauthier describes how their self-assigned task of tracking down the alleged génocidaires became all-consuming after they returned to France in 1997 with witness accounts incriminating a Hutu priest, Wenceslas Munyeshyaka, which they handed to a lawyer. "But nothing happened," he says. Then, following the trial in Belgium of four génocidaires, they decided to set up their association dedicated to tracking down the suspects in France.
"We spend all our waking hours on this. We never see our friends," he says.
The couple return regularly to Rwanda, where they are faced with the challenge of a lack of documents and archives. "But if you can find 10 or 15 people who all say the same thing, that's pretty good," says Mr Gauthier.
The international community let Rwanda down by failing to act to stave off the genocide. The former UN Secretary-General Kofi Annan has apologised, as has the former US President Bill Clinton. But France's relations with Rwanda, over its support for the Hutus trained and armed by the French against invading English-speaking Tutsi rebels who have ruled the country since the genocide, have remained fraught. When France launched Operation Turquoise in the west of the country in 1994, it was widely perceived as protecting the Hutu génocidaires.
Relations deteriorated further in 2006 after a French investigating magistrate accused President Paul Kagame, the former Tutsi rebel leader, of masterminding Mr Habyarimana's assassination, and Rwanda severed ties. They were restored three years later. In 2010, then President Nicolas Sarkozy acknowledged during a visit to Rwanda that "serious errors" had been made by France, but refrained from a full apology.
Mr Gauthier says that the most significant change for his association came in 2012, when five examining magistrates were appointed to look into the cases of the Rwanda genocide suspects in France.
But he senses that even now, France's fundamental political position has not changed. "France has not extradited a single suspect to Rwanda," he says. French authorities refused to extradite Mr Simbikangwa and have turned down 15 extradition requests from Rwanda which has been ruled since 1994 by Mr Kagame. The Hutu ringleaders of the ethnic massacres have been tried by a special UN-backed court which has heard more than 70 cases.
"French prosecutors haven't pursued anyone. It has all been done by the civil plaintiffs," says Mr Gauthier.
Among the suspects on the association's case list is Agathe Habyarimana, the widow of the dead President and an anti-Tutsi extremist, who was airlifted from the capital of Rwanda, Kigali, by the French following her husband's assassination. She now lives in a Paris suburb. "She shouldn't be here," says Mr Gauthier. "She was refused political asylum." Last month she appealed to the European Court of Human Rights, prompting Mr Gauthier to write a letter of complaint to the Interior Minister, Manuel Valls.
"I don't think France's relations with Rwanda are particularly good now. No senior politicians have gone to Rwanda," says Mr Gauthier. It remains to be seen who will represent France at the 20th anniversary commemorations of the genocide in Kigali on 7 April. Mr Gauthier stresses that the trial of Mr Simbikangwa, seen as a first major step towards future prosecutions, is not that of France.
The verdict is expected on 14 March.