A witness in the upcoming trial of alleged Nazi death camp guard John Demjanjuk is under preliminary investigation for similar crimes, Spiegel magazine reported on Sunday.

The 88-year-old, named only as Samuel K., is "suspected of assisting in the gruesome murder of at least 434,000 people" while a guard at the Belzec death camp in Nazi-occupied Poland in World War II, Spiegel said.

Demjanjuk, 89, goes on trial on November 30 in Munich on charges of assisting in the murder of 27,900 Jews and others while a guard at another death camp, Sobibor.

Demjanjuk's family say he is innocent but K., who like Demjanjuk was taken prisoner by the Germans while in the Red Army and recruited by the SS to work as a guard, has fully admitted several times being at Belzec, Spiegel said.

"It was clear to us all that Jews were killed there and were later burned too. We could smell it every day," the magazine cites him as saying.

After World War II, Ukrainian-born Demjanjuk moved to the United States where he worked as an auto mechanic. K., meanwhile, took German citizenship and has been a free man for the past six decades.

Investigators preferred to concentrate on bigger fish in the Nazi killing machine, but the case of Demjanjuk, deported from the United States in May, has triggered a change in policy, Spiegel said.