Two former Rwandan mayors go on trial in France on Tuesday facing charges of crimes against humanity and genocide over the 1994 massacres in the central African country.
As the second trial in Paris by a special court created to go after suspected Rwandan killers who fled to France, it is expected to lay bare the strained relations between the two countries.
Two decades on, Rwanda accuses France of complicity in the genocide -- which saw at least 800,000 people die in an 100-day slaughter -- because of its unwavering support for the Hutu nationalist government at the time.
Two years ago, on the 20th anniversary of the mass killings, Rwanda's minority Tutsi president, Paul Kagame, openly accused French soldiers of not only complicity in the genocide but of actually taking part in it.
On Tuesday, Octavien Ngenzi, 58, and Tito Barahira, 64, will go on trial for allegedly playing a direct role in the massacre of hundreds of Tutsi refugees in a church in the eastern town of Kabarondo on April 13, 1994.
The pair were sentenced in absentia to life imprisonment by Rwandan people's courts, known as gacaca, in 2009.
They were both mayors of Kabarondo, Ngenzi having succeeded Barahira in 1986.
They deny accusations of carrying out "massive and systematic summary executions" and implementing a "concerted plan aimed at the annihilation" of the Tutsi minority.
Their lawyers Philippe Meilhac and Francoise Mathe have highlighted "contradictions" in witness testimony.
Meilhac has also said he is "extremely concerned" over Barahira's fitness to stand trial, as he suffers from kidney failure and must have dialysis three times a week.
The killings in Kabarondo, a town near the border with Tanzania, took place with great speed.
The bloodshed was over by the end of April, when Tutsi rebels in the armed wing of what is now the ruling Rwandan Patriotic Front (FPR) took control of the area.
Elsewhere in the former Belgian colony, the slaughter would continue until the FPR fighters finally prevailed in July.
The mayors' trial, which is set to last eight weeks, comes two years after that of Pascal Simbikangwa, a former Rwandan army captain who was jailed for 25 years for his role in the genocide.
The defence has denounced that verdict as "political" and is appealing it.
"With this second trial, we will be dealing with a much more concrete genocide, with victims," said Alain Gauthier, president of the Collective of Civil Plaintiffs for Rwanda (CCPR).
"There are around 50 witnesses coming from Rwanda," Gauthier, whose wife lost her mother and dozens of other relatives in the genocide, told AFP.
- A 'good mayor' -
Witnesses have said that on the morning of April 13, they saw Barahira, wielding a spear, at a rally at the football field where he called for "work" -- then already code for killing Tutsis.
Soon afterwards, hundreds of refugees who had arrived in the previous days were hacked or beaten to death or blown up with hand grenades within the space of a few hours, according to survivors.
They say Ngenzi and Barahira took part in the process of separating the Tutsis from the Hutus.
Barahira, as the town's former mayor, was said to have "exceptional influence", his lawyer said, adding that he "went to see if he could do something to help the refugees".
Ngenzi, accused of initial passivity before taking on an active role, is described by his lawyer as "a good mayor overwhelmed by events".
He has been held since 2010 when he was captured in the French overseas department of Mayotte off the east coast of Africa, where he had been living under a false name.
Barahira was arrested in 2013 in the southwestern French city of Toulouse where he was living.
- 'Time on killers' side' -
Gauthier's non-profit CCPR is devoted to tracking down alleged perpetrators of the genocide who fled to France.
Likened by some to a Nazi hunter, he says his task is a race against time.
"We're well aware that it is going to be more and more difficult to try people. More than 20 years after the genocide some witnesses contradict each other, or they're vague... Time is on the killers' side," he said.
Kigali broke off ties with Paris in 2006 after a French judge issued arrest warrants against nine Rwandan officials over the assassination of Hutu president Juvenal Habyarimana.
The shooting down of the presidential plane on April 6, 1994, was blamed on the Tutsis and is considered to be the event that sparked the genocide.
The diplomatic freeze lasted for three years.
Last year, charges were thrown out against a priest, Wenceslas Munyeshyaka, the first Rwandan to be prosecuted in France in what had also been viewed by his defence as a politically motivated case.