Rwandan President Juvenal Habyarimana was killed when his plane was shot down in April 1994. That incident is said to have sparked the genocide that left roughly 800,000 ethnic Tutsis and moderate Hutus dead in a bloody 100-day campaign.
Theogene Rudasingwa, a former ally of Kagame living in the United States, told the BBC he overhead Kagame say in 1994 that he ordered the downing of Habyarimana's plane.
"He has fully understood that an action like that one might trigger consequences which, as we know, in our country and the Great Lakes region actually produced that crime of genocide," Rudasingwa told the broadcaster.
Kagame led rebel forces in the Tutsi-led Rwandan Patriot Front in the capture of the Rwandan capital that put an end to the Hutu assault on Rwandans.
Kagame in 2006 was accused by a French court of killing Habyarimana, a charge he shrugged off as ridiculous.
He secured a second term as president in a 2010 election. He won his first term as president in 2005 with 95 percent of the vote.
Last week, the trial chamber at the International Criminal Tribunal for Rwanda, in Tanzania, sentenced former ministers Justin Mugenzi and Prosper Mugiraneza each to 30 years in prison for conspiracy to commit genocide and direct and public incitement to commit genocide.