German prosecutors said that Demjanjuk, 89, worked as a guard at the Sobibor death camp in Nazi-occupied Poland in 1943. Sobibor was an extermination camp rather than a concentration camp, which meant that Demjanjuk would have been involved in mass murder, prosecutors argued.
Demjanjuk appeared in court in a wheelchair with his eyes closed and covered in a blanket. Family members said he was too sick to stand trial. However, doctors deemed him fit enough to stand trial, but only in two 90-minute sessions per day.
According to The Wall Street Journal, Demjanjuk was previously convicted in 1988 of war crimes and crimes against humanity. He spent seven years in prison until his conviction was overturned in 1993, when Israel's Supreme Court found that Demjanjuk had been mistakenly identified as someone else.
Though there are no living witnesses to testify against Demjanjuk, prosecutors say they can convict Demjanjuk using an SS identity card and orders sending him to Sobibor from the Trawniki training camp for Nazi guards. However, defendants question the authenticity of the documents.
The Wall Street Journal reported that Demjanjuk has been stripped of his U.S. citizenship and was deported from the country in May.
If convicted he could face up to 15 years in prison. The trial will resume Tuesday.