A 50-year-old doctor from Saudi Arabia, Taleb al-Abdulmohsen had expressed anti-Islam views and described himself as a Saudi dissident, a German official said.
Rwanda tries to silence critics abroad by targeting relatives back home, at times arresting and torturing them, say former officials and other exiled Rwandans.
In 1983, he reported that he had found the diaries of Adolf Hitler -- a "scoop of the century" that was the mistake of a lifetime. The diaries were forged.