Authorities say they discovered the identity of a former Nazi concentration camp who was living for decades in the US after investigators saw an index card found in the wreckage of the SS Thielbek, a bombarded German ship that was lifted from the Baltic seabed.

The federal government said Thursday that it is deporting Friedrich Karl Berger, a 94-year-old German ex-Nazi who has been in Oak Ridge, Tennessee, for decades.

An immigration judge ordered Berger's deportation on February 28 after a two-day trial in Memphis, authorities said.

It's unclear when he will be removed. Berger has 30 days to appeal the ruling.

The government says Berger was an armed guard at a concentration camp near Meppen, Germany, in 1945.

Federal prosecutors say that they confirmed Berger’s identity thanks to an index card that was found submerged in a sunken ship, The Washington Post reported.

US authorities confirmed the identity of a Nazi concentration camp guard after a sunken German ship, SS Thielbek (above), was refloated from the bottom of the Baltic Sea. Amid the wreckage were index cards that contained information about personnel at the camps

Friedrich Karl Berger was said to have been 'willing' to work at a Neuengamme sub camp. The main concentration camp in Hamburg is pictured

The ship was destroyed at the port of Lubeck, where survivors are seen above in 1947

Prisoners were held in Neuengamme during the winter of 1945 in 'atrocious' conditions

The immigration judge found that the prisoners Berger guarded were held in atrocious conditions and were exploited for forced labor.

Neuengamme’s inmates included Russian, Dutch, Polish, and Jewish civilians as well as political opponents from Italy, France, and other countries.

In March 1945, British and Canadian forces moved closer to the subcamp.

The Justice Department says that Berger helped guard prisoners who were forced to evacuate to the main camp.

During the two-week trek, 70 prisoners died as they traveled in inhumane conditions, according to two government news releases.

The prisoners were forced to live in 'atrocious' conditions and work 'to the point of exhaustion and death,' according to removal orders issued in 1945.

At the end of the forced march, hundreds more prisoners were believed to have been killed after they were loaded onto three ships that were anchored in the Bay of Lubeck.

One of the ships, the SS Thielbek, was a cargo steamship that was sunk by the British Royal Air Force on May 3, 1945.

Some 2,750 people on board, including prisoners from the Neuengamme, Stutthof, and Mittelbau-Dora concentration camps, died in the bombardment.

The sunken vessel was then refloated in 1949.

The index cards containing information about Berger’s service in the German Navy were found inside the wreckage of the Thielbek.

American prosecutors say that the index cards were transcribed.

The RAF was apparently unaware that there were prisoners on board the ship.

The Thielbek and another vessel sunk, according to investigators.

The ship held some 2,000 index cards that contained information about personnel who worked at the camps, including Berger, according to the Justice Department.

‘What are the odds, you know, of that card having survived... and making it to us decades later?’ said Eli Rosenbaum, the Justice Department prosecutor who helped oversee the case.

DOJ prosecutors and historians delved deeper into the case, unearthing evidence in Germany, Denmark, England, Poland, and Russia.

The investigation was also aided by the United States Holocaust Memorial Museum.

Berger acknowledged that he never requested a transfer from the concentration camp guard service and that he still gets a pension from Germany.

Widower Berger, who came to the US in 1959 with his wife and daughter and has two grandchildren, told The Washington Post: 'After 75 years, this is ridiculous. I cannot believe it. I cannot understand how can happen in a country like this. You’re forcing me out of my home.

'I was 19 years old. I was ordered to go there.'

It was not clear why Berger now faces court action or what German authorities will do on his return to the country.

DailyMail.com has contacted the Department of Justice for comment.

The Justice Department says Berger entered the country legally in 1959.

SS guards at the Neuengamme concentration camp celebrate Christmas in 1943

With the advance of Allied forces Berger even helped guard the prisoners during their forcible evacuation to the Neuengamme main camp, pictured, after the Nazis abandoned the sub camp

Just two years earlier, a federal law that barred entry to those who helped Nazi persecution expired.

In 1978, Congress passed a law that barred anyone who helped the Nazis persecute their victims from entering or living in the US.

The US Department of Justice's Human Rights and Special Prosecutions unit launched an investigation into Berger in 2017.

The Immigration and Customs Enforcement's Human Rights Violators and War Crimes Center also investigated.

In August 2018, American authorities deported a 95-year-old former Nazi concentration camp guard who had lived quietly in New York City for decades. The man died in Germany about five months later.

Assistant Attorney General Benczkowski said in a statement: 'This ruling shows the Department's continued commitment to obtaining a measure of justice, however late, for the victims of wartime Nazi persecution.'

Immigration and Customs Enforcement assistant director David C. Shaw said: 'This case is but one example of U.S. Immigration and Customs Enforcement's commitment to ensuring that the United States will not serve as a safe haven for human rights violators and war criminals.

'We will continue to pursue these types of cases so that justice may be served.'