Guy Theunis was transferred to Belgium from a Rwanda jail last year after he was accused of being an accomplice to the mass killings, Expatica reported.
"I am no judge. But the information and pieces of evidence that I have been able to look at appear to prove his guilt," Kagame told the newspaper Jeune Afrique/L'intelligent.
Theunis was the first foreigner to be brought before a Rwandan village court set up to investigate the genocide that killed 800,000 Tutsis and moderate Hutus in 1994.
Theunis denies charges that he incited genocide through republishing articles from the extremist publication Kangura in his Dialogue magazine, of which he was editor-in-chief from 1989-94.
He says he personally wrote articles to press for human rights and that the translated Kangura articles only ever appeared as part of a press review, Expatica reported.