An index card submerged in Baltic Sea has helped lead to the prosecution of a Nazi collaborator in United States.

Seventy-five years after the end of World War II, a US immigration judge in Memphis ordered the deportation of a longtime Tennessee resident and German citizen who acknowledged having served as a guard at a concentration camp in Germany and was still receiving a pension for work that included his wartime service.

According to the removal order, announced by the US Justice Department and Immigration and Customs Enforcement on Thursday, Friedrich Karl Berger served at a subcamp of the Neuengamme concentration camp system, near Hamburg.

The camp held Russian, Dutch and Polish civilians, as well as Jewish prisoners and political opponents from France, Italy and other countries.

In the winter of 1945, according to the removal order, prisoners were forced to live in "atrocious" conditions and work "to the point of exhaustion and death."

In March 1945, as British and Canadian forces approached the subcamp, Berger helped guard prisoners forced to evacuate to the main camp, Justice Department officials said.

During the brutal, two-week trek, 70 prisoners died. Hundreds more were killed when they were placed on two ships at anchor in the Bay of Lubeck, in the Baltic Sea, that were mistakenly bombed by the British Royal Air Force in May 1945 during the last week of the war.

US Justice Department historians were able to document Berger's service at the camp in part with information from an index card found in one of the sunken ships several years after the bombing.

The card summarised Berger's work in the camp system.

After the war, Berger emigrated from Germany to Canada with his wife and daughter, and came to the United States in 1959.

"If you had told me even a couple of years ago that I would find myself in February 2020 - last week - cross-examining a former Nazi concentration camp guard in an American courtroom, I would have found that difficult to believe," said Justice Department prosecutor Eli Rosenbaum, who helped oversee the case and has spent years at the department investigating and prosecuting Nazi war criminals in the United States.

Reached by phone, Berger, now 94, said he was ordered to work in the camp, was there for a short time and did not carry a weapon. In the United States, he said, he made a living building wire-stripping machines. He is now a widow with two grandchildren.

"After 75 years, this is ridiculous. I cannot believe it," he said. "I cannot understand how this can happen in a country like this. You're forcing me out of my home."

According to the Justice Department, Berger worked in the German navy. He was detailed to the concentration camp in the last months of the war. When prisoners were evacuated, they were placed on three ships at the German port city of Lubeck.

The British Royal Air Force, unaware that thousands of prisoners were being held, bombed from the sky. Two of the ships sank.

When the Germans raised one of the ships a few years later, they found more than 2000 index cards with personnel information for Berger and others.

"What are the odds, you know, of that card having survived . . . and making it to us decades later?" Rosenbaum said.

Prosecutors and former and current Justice Department historians found more evidence in Germany, Denmark, England, Poland and Russia. Officials at the US Holocaust Memorial Museum also supported the investigation.

During the two-day trial in immigration court, held last week, Berger acknowledged that he guarded prisoners, did not request a transfer from the camp and was still receiving a pension from Germany for work based in part on his wartime service, US officials said.

Berger said much of what was determined in court was based on "lies."

"I was 19 years old," he said. "I was ordered to go there."

In 1946, British authorities charged four top officials at the camps with war crimes.

One escaped before trial, another was hanged and two others were imprisoned.

One of the lead British investigators, according to the Justice Department, was Captain Anton Walter Freud, a grandson of Sigmund Freud, who had escaped Vienna with his family in 1938.

One of the British military judges was Earl Edward John Spencer, whose daughter Diana would go on to become the Princess of Wales.

US Justice Department officials said Berger came to the United States legally; the federal law that barred the entry of people who assisted in Nazi persecution had expired in 1957.

When he applied to immigrate to the US, Berger disclosed that he had been a member of the German navy.

US immigration Judge Rebecca Holt ordered Berger removed under a 1978 law, known as the Holtzman Amendment, that bars anyone who participated in Nazi-sponsored persecution from entering or living in the United States.

Berger has 30 days to appeal the decision to the Board of Immigration Appeals in Falls Church, Virginia.

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