An 84-year-old immigrant accused of participating in the 1994 Rwandan genocide went on trial Tuesday in an immigration case that the Justice Department says is the first of its kind in the U.S.

His case — which hinges on whether Lazare Kobagaya committed atrocities in Rwanda and therefore lied when he told U.S. immigration authorities that he had never committed a crime — is the first criminal prosecution in the United States requiring proof of genocide, according to the U.S. Justice Department.