Last year a German court sentenced the Ukrainian-born man to five years in prison in connection with the six-month period he was a guard in Poland at the Sobibor death camp in 1943.
Demjanjuk vigorously denied the charges and appealed his conviction, arguing throughout the proceedings that he had been a victim of the Nazis, having been captured by them as a prisoner of war.
He was released pending an appeal, having already spent nearly two years in prison, as he was deemed unlikely to abscond.
After World War II, Demjanjuk went to live in the United States, raising three children there and working in the auto industry. After a legal case brought in Israel in 1986 collapsed, he returned to the United States.
But he was stripped of his citizenship in 2002 for lying about his past and finally deported from the United States to Germany in 2009 to face trial.
His son - who insists Demjanjuk died a scapegoat and a victim - filed a complaint with Bavarian prosecutors asking for an investigation of several doctors and a nurse on suspicion of manslaughter and other charges.
The complaint says that doctors administered a drug called Novalgin which has severe side effects, alleging a "medical execution."
Officials in Germany were not immediately available for comment as their offices had closed for the day.
- AFP