Auschwitz prison guard Oskar Groening claims he stood idly by when doctors at his death camp decided who among the thousands of Jews were fit for work — and who would be slaughtered.

The former SS sergeant knew the horrors of the Holocaust firsthand, but on his second day of testimony Wednesday in a German courtroom, he remained adamant that he never personally chose who should be killed during the Nazi atrocities of World War II.

Instead, he has said, he is merely “morally complicit.”

"Whether I am legally guilty under criminal law, you will have to decide," the visibly frail 93-year-old earlier told judges hearing his case in Lueneburg, northern Germany.

The outcome of the trial hinges on whether Groening, who worked as a so-called "accountant" at the Auschwitz concentration camp from 1942 to 1944, can still be an accomplice to murder even though there is no evidence linking him to a specific death. Holocaust experts following the case say Groening will have a hard time proclaiming his "legal" innocence when German prosecutors are vigorously going after those they consider guilty by association.

"It is an attempt by the Germans to deal with the fact that genocide is an organized crime that is perpetrated collectively."

Groening "was part of the killing machinery," said Norman Goda, a University of Florida historian who has researched World War II war crimes. "His job was to inventory the piles of cash and stolen goods of the murdered, which was sent back to Berlin. He was hardly insignificant to the enterprise — robbing murdered Jews was an integral part of the destruction process."

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If found guilty, Groening faces a maximum sentence of 15 years in prison — time that he would presumably spend a fraction of serving because of his age.

'Auschwitz bookkepper' tells court of grisly mass murder he witnessed at death camp http://t.co/ct3Yx5E5yv pic.twitter.com/YzkcZ0X6f6 — ITV News (@itvnews) April 21, 2015

His trial is the first to test a new line of German legal reasoning that has unleashed an 11th-hour wave of new investigations of Nazi suspects. Prosecutors argue that anyone who was a death camp guard can be charged as an accessory to murders committed there, even without evidence they were involved.

There are currently 11 open investigations against former Auschwitz guards, and charges have been filed in three of those cases, including Groening's.

Groening joined the SS by choice. On Tuesday, he testified that he did not know what his duty would be until he arrived at Auschwitz — but quickly learned that Jews were being selected for work and those who couldn't work were being killed. In the vocabulary of the camp, he said, "the enemies of Germany were being exterminated."

The case against Groening has precedence after a Munich court in 2011 found Ukrainian-born Ohio resident John Demjanjuk — a former SS guard — guilty as an accessory to murder during the Holocaust. Prosecutors were able to nail him based on his position working in Sobibor, Poland, where about 250,000 people were exterminated.

The Demjanjuk case "opened up new avenues for prosecuting cases where previously conviction would have been unlikely," said Devin Pendas, a professor at Boston College who has studied Nazi war trials. "Demjanjuk died before his appeal could be decided, so we don't know yet whether this theory will actually hold up on review, but the prosecution in the Groening case is going to give it a shot."

Pendas said the prosecution can argue that the death camps were, in their entirety, designed for the sole purpose of mass murder, and therefore, anyone whose contribution was indispensable for the extermination operations can be considered co-perpetrators of murder.

"It is an attempt by the Germans to deal with the fact that genocide is an organized crime that is perpetrated collectively," Pendas said.

The German government has been committed in the past couple of decades to go after not only those who played a major part in the Holocaust, but also "ordinary people" who helped Auschwitz and other notorious Nazi death camps function, Goda added.

Germany has no statute of limitations for these Holocaust-related crimes.

"Whether a particular (SS) officer was a sadist with a blood lust or a careerist who in normal times would have done something else with his life is not the point morally and not the point legally," Goda said. "The Final Solution was loaded with people who 'did not kill anyone.' In fact, it could not have functioned without them."

The Associated Press contributed to this report.