The Stuttgart court said on Wednesday that Murwanashyaka's health deteriorated suddenly on April 11. He was transferred to a hospital, where he later died. The court declined to provide further details, citing patient confidentiality.
The FDLR's vice president, Straton Musoni, was given an eight-year sentence for his role in the group. That verdict wasn't overturned. Murwanashyaka's lawyers argued during the trial that he had merely been the group's political figurehead and hadn't controlled its military wing.
Prosecutors in Germany, where Murwanashyaka had lived since the 1980s, argued he had issued remotely instructions to FDLR members in Congo by phone, text message and email. The group carried out killings in the Congolese villages of Mianga, Busurungi, Chiriba and Manje in 2009.
The rebel group is made up mostly of Hutu refugees from Rwanda who took shelter in neighboring Congo after the 1994 genocide in which over 800,000 people were killed, most of them ethnic Tutsis but also moderate Hutus.