After a French-crewed plane carrying Juvenual Habyarimana was shot down with a missile on April 6, 1994, a campaign targeting Rwanda's Tutsi population was unleashed. Within 100 days, some 800,000 people had been slaughtered.
The Rwandan former (1994-2002) army chief of staff whom French investigating magistrates want to question, Faustin Kayumba Nyamwasa, lives in exile in South Africa, where he has survived at least two attempts on his life.
He is the subject of a previous French arrest warrant and has also been sentenced to 24 years in jail by a Rwandan court.
Like President Paul Kagame, he was a founder member of the rebel Rwandan Patriotic Front (RPF) which took power in the central African country in late 1994, putting an end to the genocide.
In a notarised deposition submitted to the French investigation in June this year, Nyamwasa denied witness testimony that tied him to the shooting down of Habyarimana's plane, and said Kagame had instigated the attack, which also claimed the life of the then president of Burundi.
In his deposition, Nyamwasa said that on April 6, 1994 he heard Kagame himself say that "Habyarimana's plane was brought down by our own (RPF) forces".
The deposition led French investigating magistrates to formally ask South Africa for its cooperation in having Nyamwasa questioned, according to case sources.
The French investigation had been effectively closed in 2014 and again in January this after previous requests to South Africa for cooperation came to nothing.
In 2006, Rwanda cut diplomatic ties with France after the investigating magistrate then in charge of the case issued arrest warrants for several people close to Kagame, including Nyamwasa.
Seven of them, including all those named in Nyamwasa's deposition, were later charged in France but have since called for the cases against them to be dropped.
A lawyer for the seven dismissed the latest move by the investigating magistrates as "yet another delaying tactic designed to put off the inevitable dismissal" of the cases and to derail Kagame's bid for a third term in next year's presidential election.
Kagame's camp maintains that the testimony given to French investigators by expert witnesses -- which identified an area held by Habyarimana's presidential guard as the most likely place from which the missile was fired -- is evidence of his innocence.
Kagame has long maintained that Habyarimana was killed by Hutu hardliners unhappy with the concessions the then president was making during negotiations with the RPF rebels.
Kigali has also repeatedly accused Paris of having a hand in the genocide and of being slow to prosecute some of its kingpins living in France.