Investigators in Oberbayern-Sud said they were conducting a routine probe into the one-time concentration camp guard's death at a nursing home.
Demjanjuk was appealing a 5-year prison sentence for assisting in mass murder while a guard at the Sobibor camp in Poland during World War II. CNN said the National Holocaust Museum in the United States estimates that at least 167,000 people died at Sobibor during the war.
Demjanjuk moved to Ohio after the war and worked quietly as an auto worker until the late 1970s when allegations arose that he was actually a particularly feared guard nicknamed Ivan the Terrible. His U.S. citizenship was revoked for a second time in 2002 and he was finally extradited to Germany to face trial in 2009.
Demjanjuk, a native of Ukraine, argued he spent the war as a prisoner himself who was forced to work at Sobibor by his German captors.