The trial this week of a Rwandan genocide suspect in a Paris courtroom is a well-earned victory for the French human rights groups who lobbied so hard and so long for justice. The milestone trial signals the end of France as a safe haven for génocidaries.

 But more than this, the trial is likely to see intense public scrutiny of one of the great scandals of the past century – the role of France in the 1994 genocide of the Tutsi of Rwanda, which for 20 years journalists and activists have tried so hard to expose.

Pascal Simbikangwa, the defendant in Paris, is said to have been a member of an inner circle of power in Rwanda that devised genocide as a planned political campaign. Developed by Hutu ideologues, it was intended to prevent a power-sharing system of government that was to include the Tutsi. The genocide claimed up to a million lives.

A captain in the Rwandan gendarmerie until 1986, when he was paralysed in a car accident, Simbikangwa – a fanatic who hoped to create what was known as "a pure Hutu state” – worked for the security services in the capital Kigali.

He was eventually found hiding out in the French department of Mayotte, an island group in the Indian Ocean, with 3,000 forged identity papers – more than enough for the hundreds of Rwandan fugitives still at large. He denies all the charges, and his lawyer says he is a scapegoat.

Until now there has been a complete absence of will in Paris to bring to justice any of the estimated 27 Rwandan genocide fugitives who live on French soil.

The country was a staunch ally of the Rwandan government which planned and perpetrated the genocide. The trial may well show the French electorate just how appalling its secret policy towards the central African state really was.

The policy was devised in secret, with no accountability from press or parliament and largely determined within the confines of a special office in the president’s Elysée Palace known as the Africa Unit.

It operated through a network of military officers, politicians, diplomats, businessmen and senior intelligence operatives. At its heart was President François Mitterrand, who had operated through senior army officers: General Christian Quesnot, Admiral Jacques Lanxade and General Jean-Pierre Huchon.

The prosecution testimony in the trial will be unprecedented in the detail it will provide about the genocide. The evidence combines the results of investigations into the Simbikangwa case at the International Criminal Tribunal for Rwanda (ICTR), and details from investigations carried out by Rwandan authorities.

Never before, not even in the courtrooms of the ICTR, has such an impressive array of witnesses assembled. It is hoped that their combined testimony will put paid to a campaign of denial waged by defence lawyers at the ICTR who claimed the killing in Rwanda was not the result of a conspiracy but was somehow "spontaneous”.

Simbikangwa’s prosecutors are concentrating on his role during the killing, when he allegedly encouraged the murder of Tutsi by Interahamwe militia on roadblocks and provided them with weapons. The roadblocks and the Interahamwe were an integral part of the planned killing mechanism and ensured the speed and scale of the slaughter.

But the impact of the Simbikangwa trial will be felt far beyond the courtroom. It is hoped that for the French public the nature of the genocide will be laid bare, and that at long last a debate about France and Rwanda will begin. Twenty years too late, a true reckoning may at last be possible.

The writer is an investigative journalist and author; she is the author of A People Betrayed: The Role of the West in Rwanda’s Genocide (2000), and Conspiracy to Murder: The Rwanda Genocide (2004)

This article was first published by The Guardian newspaper