A former Nazi accountant, known as the "bookkeeper of Auschwitz," asked for forgiveness during his trial on Tuesday in Lueneburg, Germany.

Oskar Groening is a former SS officer charged with 300,000 counts of accessory to murder for his role in the brutal Nazi regime that caused the deaths of millions of people.

The 93-year-old admitted that he volunteered to join the SS because he "wanted to be part of it," but claimed he initially was unaware of the gas chambers used to exterminate prisoners at the Auschwitz-Birkenau camp in Poland.

Groening's roles were to sort and count the money taken from the prisoners, and guard their luggage when they arrived at the camp by train.

Prosecutor Jens Lehmann said the bookkeeper made "at least a low-level contribution" to the "smooth operation" of the concentration and extermination camp.

Soon, he did witness atrocities, including the brutal death of a baby that he recounted on the witness stand. Groening has also provided media interviews about his experience at the death camp.

"I saw everything," he wrote in 1985. "The gas chambers, the cremations, the selection process... I was there."

Groening faces 15 years in prison for working at the camp, although he denied physically harming any prisoners at Auschwitz.

"For me there's no question that I share moral guilt," he told his judges. "I ask for forgiveness... You have to decide on my legal culpability."

Nearly 70 Holocaust survivors and family members of victims attended Groening's trial. A Romanian-born survivor, 81-year-old Eva Kor, said that Groening "is a murderer because he was part of the system of mass murder."

The defendant acknowledged the evil that led to the deaths of some 1.1 million people at the Auschwitz-Birkenau camp, and over six million during the Nazi regime.

"What kind of hatred was behind it?" he said of the Holocaust. "I just can't understand it."

Groening's trial is scheduled to end on July 29.