A former captain in the rebel movement, the Rwandan Patriotic Front (RPF), says he was ordered to provide security as missiles were fired at the plane carrying the presidents of Rwanda and Burundi.
By Martin Plaut
BBC regional analyst
Captain Josue Abdul Ruzibiza says he was ordered to secure an area close to Kigali airport.
It was the assassination of the two presidents that unleashed the genocide that left 800,000 people dead.
Some 800,000 people were killed in the 1994 genocide
The former leader of the RPF, President Paul Kagame, is currently in Belgium as part of a European tour, and has dismissed accusations of his involvement in the killing of the two presidents as "invented".
Captain Ruzibiza arrived in the Rwandan capital, Kigali, in December 1993.
He was part of the RPF battalion sent to the city to guard the movement's MPs and ministers, who were joining the transitional government being formed under a peace agreement signed in Arusha.
Capt Ruzibiza told the BBC two missiles were brought from Parliament House, where the battalion was being housed.
As the plane carrying the two presidents came in to land, the missiles were fired.
"The missile didn't hit the engine and so didn't cause the plane to roll over. It was the second missile that that hit the engine. The first one hit the wing, and the plane could still land. But the second one finished the plane off," said Captain Ruzibiza.
His account comes after the result of a French judicial enquiry was leaked earlier this week, blaming the downing of the plane on President Paul Kagame, who was then the leader of the RPF.
The report has been dismissed as propaganda by the Rwandan authorities.
But it fits with the Capt Ruzibiza's testimony.
He says the two men who actually fired the missiles are now senior officers in the Rwandan presidential guard and military intelligence.
Asked why he had kept quite so long, Captain Ruzibiza - who is now in exile - said he has lived in fear of his life.