German prosecutors have reopened the case files of hundreds of former Nazi death-camp guards under a new precedent set by the conviction of John Demjanjuk.

The Ukrainian-born Demjanjuk, who is now 91, was a guard at the Sobibor death camp in Poland. In May, he was sentenced to five years in prison as an accessory to the murders of more than 28,000 people at the camp. After his conviction, he was freed pending appeal.

The verdict against Demjanjuk set a precedent as the first time prosecutors were able to get a conviction in a Nazi-era case without direct evidence that the defendant took part in a specific murder. In July, Bavarian prosecutors opened a new case against Demjanjuk, saying he was responsible for the deaths of nearly 5,000 people at the Flossenbuerg concentration camp in Germany.

Demjanjuk has denied playing any role in the Holocaust. He testified that he was drafted into the Soviet army in 1941 and was later a German prisoner of war who was assigned to work as a prison camp guard.

After the war, Demjanjuk became a U.S. citizen and spent decades working as a mechanic before being deported to Germany in 2009 to face trial.