German car giant Audi’s predecessor company used slave laborers from concentration camps during World War II on a massive scale, a new report has found.

An historical investigation commissioned by the company — the last German auto company to do so, preceded by Volkswagen, Daimler and BMW — found that when Audi was operating under the name Auto Union, it struck a deal with the SS, by which more than 3,700 inmates from Nazi concentration camps were put to work for the company.

The 500-page report, authored by historians Martin Kukowski and Rudolf Boch and published Monday, revealed that the Nazi SS divisions built seven labor camps for this purpose.

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Another 16,500 laborers — not interned in concentration camps — also were made to work for the car company in the Saxon cities of Zwickau and Chemnitz, in addition to 18,000 at a plant in Bavaria where more than 4,000 died, the report noted.

“More than 20,000 forced laborers were used in the production of Auto Union in their Saxon works, including almost one-fifth from concentration camps,” said the study authors, who also found that disabled workers were sent to concentration camps to be executed.

During the war, some of Audi’s plants were turned over for military production of tanks and aircraft engines.

Kukowski and Boch, basing their report on access to Audi archives, said that Auto Union’s management bore “moral responsibility” for the exploitation of slave labor, focusing particularly on founder, Dr. Richard Bruhn, a Nazi party member.

Bruhn was Auto Union’s chairman of the board from 1932, when the company was founded, until 1945, and again after the company was reestablished post-war.

Bruhn, heralded on Audi’s website as the “Father of the Auto Union,” died in 1964.

The study’s findings came as a shock to its current management.

“I’m very shocked by the scale of the involvement of the former Auto Union leadership in the system of forced and slave labor,” Audi works council head Peter Mosch told Wirtschaftswoche, a German business news magazine. “I was not aware of the extent [of this involvement],” he added.

Auto Union merged with Volkswagen, Audi’s parent company, in 1965, dropping the original name in 1985 after a merger

According to the Daily Mail, a decade ago, Audi paid millions into a fund set up by the German auto industry to compensate Nazi slave laborers and their descendants.