By Mark Doyle
BBC World Affairs correspondent
President Kagame has always accused France over the genocide
The question of who shot down the plane carrying the former president of Rwanda in April 1994 could turn out to be one of the great mysteries of the late 20th Century.
The act served as a catalyst for the genocide of some 800,000 (others say as high as one million) people in just 100 days.
A French investigative judge, Jean Louis Bruguiere, has accused the ethnic Tutsi rebel leader at the time, Paul Kagame, of having been responsible.
Mr Kagame, now Rwanda's president, was furious and broke off diplomatic relations with France.
Judge Bruguiere mounted the inquiry in France because the families of the French aircrew, also killed when the plane went down, laid a judicial complaint.
When the Rwandan president's Mystere Falcon executive jet was blown out of the skies over Kigali airport at about 2000 local time on 6 April 1994, it was the beginning of a bloody nightmare for Rwanda.
The ethnic Hutu president, his aides and his French air crew were all killed.
Within minutes, on the ground, extremist Hutu army officers and their militias began taking revenge on the minority Tutsis and other government opponents.
The Rwandan genocide had begun.
The extremist Hutus blamed Tutsi rebels, led by Paul Kagame, and Belgian mercenaries, for downing the plane.
But others, including senior United Nations officials present on the ground suspected that Hutus, or mercenaries working for them , may have carried out the attack in order to stop the late president signing a compromise peace deal with the Tutsi rebels.
France backed the Hutu government at the time.
A British expert on the Rwandan genocide, Linda Melvern, author of the investigative study Conspiracy to Murder, says she is surprised at the lack of convincing new evidence in the French judge's allegations given that, at the time of the shooting down of the plane, France had very close relationships in the region.
1994: RWANDA'S GENOCIDE
6 April: Rwandan Hutu President Habyarimana killed when plane shot down
April -July: An estimated 800,000 Tutsis and moderate Hutus killed
July: Tutsi-led rebel movement RPF captures Rwanda's capital Kigali
July: Two million Hutus flee to Zaire, now the DRC
"At the time of the planning of the genocide the French government had 47 senior officers embedded into the Rwandan army , which subsequently played such a large role in the genocide , and the best informed government of (them) all of what was going on in Rwanda was the French," she says
Ms Melvern said the evidence the French judge had presented alleging President Kagame's involvement in the murder of his predecessor was very sparse, and that some of it, concerning the alleged anti-aircraft missiles used to down the presidential jet, had already been rejected by a French Parliamentary enquiry.
A brief look at the Judge's 64 page report, as made available on the websites of some French newspapers, also reveals that the report appears to have been written in something of a rush.
Several of the key players, including two former heads of state, have their names mis-spelt.
Anyone who has followed Rwanda in recent years, and seen the extraordinary lengths to which people are prepared to use violence, to gain and hold on to power, will accept that almost anything is possible.
I met Paul Kagame many times when he was a rebel commander, and have interviewed him since he became president.
Kagame's soldiers marched in and took control after the genocide
I have no doubt that had he wanted to down the plane he would have had the technical and military capacity to do so.
But his denials have been so vehement, so public and so consistent that they might put his domestic political credibility on the line if he is ever proven wrong.
Kagame is not overly-concerned about his international credibility - ever since the genocide he has made it clear that he has no respect for an international community which largely stood by while hundreds of thousands were killed.
Of course, the debate about who shot down the Mystere Falcon may be a purely theoretical one.
It is most unlikely that any of the accused Rwandans would make the mistake of finding themselves in France and available for arrest. Judge Bruguiere's allegations may never be tested in an independent court.
The current Rwandan government accuses France of deliberate political manipulation of the facts.
Thousands protested in Kigali this week against France
While the genocide of ethnic Tutsis and other government opponents was being carried out by the extremist Hutu regime, the then-Tutsi rebel Paul Kagame mounted a conventional war against the French-backed government.
His officers were almost all men - and a few women - who had been exiled and educated in neighbouring, English-speaking Uganda.
When he won the war, the outcome, highly unusually, led to a change in Rwanda's official second language from French to English.
Some observers believe that whatever crimes Paul Kagame may or may not have committed, the French establishment has never really forgiven him for challenging its influence in Africa.
The issue of who is responsible for downing the Mystere Falcon is not some dusty, historical problem.
The genocide, carried out just 12 years ago, is still terribly fresh in the memories of survivors. The mass killing was one of the fastest and most "efficient" pre-planned genocides of the twentieth century.
Ms Melvern sums up: "The assassination of Juvenal Habyarimana led to the elimination of the pro-democracy opposition in Rwanda. It then led to a genocide in which an estimated one million people were murdered in the space of 100 days."
"I think that although my book shows the genocide was planned beforehand (...) the trigger was this assassination."
Over the past decade the devastating political fallout of the genocide has been felt across central Africa as millions of armed refugees from Rwanda and related wars have swirled around the region.
We may never know who shot down the Mystere Falcon presidential jet.
We do know that the act of blowing it out of the sky was part of a train of events from which vast swathes of Africa have yet to recover.