The Berlin Zoo, which has been a German cultural institution for decades, has for years been hiding a dark secret: the zoo pushed out Jewish shareholders during World War II.

Over 70 years later, the Berlin Zoo is now attempting to find these former shareholders in an attempt to make amends for this unfortunate chapter in its lengthy history.

In an effort to seek out these former Jewish board members, the zoo has hired a historian, Monika Schmidt, who works for the Center for Research on Anti-Semitism in Berlin, according to the Agence France-Presse.

“Jews were very important for the zoo,” Schmidt told the AFP. “But they were pushed out step by step by the zoo itself, before the Nazi state asked any institution to do those things.”

The zoo was founded in August of 1844, according to its website. At the time of its opening, the establishment was the first such zoo in Germany and the ninth in Europe.

For decades, the zoo was a “social hotspot” for the Berlin elite, with shareholders enjoying perks such as free access and citywide prestige, reports Bloomberg. In the 1920s and 1930s, “It was ‘bon ton’ to be a shareholder of the zoo,” the zoo’s business director Gabriele Thoene told Bloomberg.

However in 1933, Nazi influence began to take its toll as the Jewish members of the supervisory board began to be forced out and replaced by members of the Nazi party, reports Bloomberg.

By 1938, all Jewish board members had been ousted and shareholders had been forced to re-sell their stock back to the zoo at a loss. This process of “Aryanization” even manifested itself physically, with signs hanging from the gates saying “Juden unerwuenscht,” (translating to “Jews not welcome”) and a complete ban on Jews by 1939, according to Bloomberg.

For years the zoo denied the existence of this Nazi chapter in its history, according to Werner Cohn, a retired sociology professor. Cohn, whose father was once a shareholder in the zoo, has made it a personal mission of sorts to get the institution to acknowledge its past.

In an open letter to Jewish stockholders posted online, Cohn states that the transfer of stock in the 1930s was “illegal and therefore invalid.”

“In brief, the Zoo was an institution in which Berlin Jews felt at home and which they supported financially and otherwise,” Cohn writes. “The Zoo, in turn, owed much to the Berlin Jews. I find it amazing that the current leadership of the Zoo has chosen to ignore this moral debt, as indeed it also tries to ignore its legal responsibilities.”

However, it appears the efforts of Cohn and others may finally be paying off. In an effort to make amends, the zoo has now commissioned a historian to track down the descendants of the ousted shareholders, according to the AFP.

“It is important to make the decision to continue to engage with this topic, to not forget what is possible,” zoo spokeswoman Claudia Bienek told the AFP, adding that reparations are not being considered.