He was found guilty for his role in the killing of eight Tutsis at the Agro-Veterinary school of Gitwe, of which he was the principal in 1994, the state-run broadcast said.
At the opening of his retrial on March 17, the defendant claimed that he had never been the school's principal and that he was in Sweden during the Rwandan genocide.
However, according to Radio Rwanda, he finally admitted that he had been running the school for three months when the genocide started.
Joseph Ntawangundi explained that there was nothing he could do to protect the victims as he was new to the school and Gitwe, hardly knowing anybody.
Detained in Kibungo's Central prison, Ntawangundi has fifteen days to lodge an appeal.
Joseph Ntawangundi is an "assistant" to Victoire Ingabire Umuhoza, the President of the United Democratic Forces (UDF, opposition) who intends to run for her party in the forthcoming presidential election scheduled for August.
Mrs. Ingabire and Mr. Ntawangundi both returned from exile in January to register their political party, created in exile. So far, they have not succeeded in doing so.
According to Radio Rwanda, Joseph Ntawangundi was arrested upon his return on the grounds of a judgment delivered in absentia by a Gacaca court in 2007. The tribunal had then sentenced him to 19 years in jail for his "complicity" in the 1994 genocide.
Back in the country, Joseph Ntawangundi was entitled to a rehearing trial.
The Gacaca courts, adapted from a form of Rwandan traditional justice, are tasked with trying suspected perpetrators of the 1994 Rwandan genocide which left some 800,000 people dead, according to the UN. These village courts, whose judges are elected from the community, can hand down sentences up to life imprisonment, which is now the maximum penalty in Rwanda. They have so far tried more than a million people.
© Hirondelle News Agency