The United States has returned seven paintings by Austrian artist Egon Schiele to the heirs of a Jewish cabaret star who possessed them prior to his 1941 death at the hands of the Nazis.

Since the 1980s, Fritz Grünbaum's family had sought the repatriation of his Schiele works. Some of the works, each valued between $780,000 (£633,000) and $2.75m, had been displayed in prestigious American museums.

Several courts filed petitions in response to the claims. A civil court in New York ruled in 2018 that Mr. Grünbaum never sold or surrendered the pieces.

On Monday, Manhattan District Attorney Alvin Bragg referred to the return of the artwork as "historic" during a ceremony.

The Museum of Modern Art (MoMA), the Morgan Library & Museum, and the Santa Barbara Museum of Art, all in New York, and the Santa Barbara Museum of Art, in California, voluntarily surrendered the stolen works to prosecutors after discovering their theft.

Several of the artifacts were also in the possession of Ronald Lauder, the president of the World Jewish Congress, and the estate of Serge Sabarsky, a well-known art collector, who both agreed to return the objects.

Mr. Grünbaum, who died in the German concentration camp Dachau, possessed 81 works by Schiele. After his arrest in 1938, his wife Elizabeth was compelled to turn over his art collection to the Nazis. In 1942, she died in a concentration center.

Adolf Hitler deemed Schiele's works to be "degenerate art" and sold them to finance the Nazi Party. Some had found their way into the hands of a New York dealer named Otto Kallir, who sold them to various purchasers.

In 2018, the heirs of Mr. Grünbaum went to court in New York State to demand the return of two Schiele works from Richard Nagy, a London-based collector. Charles V.

Ramos, the presiding judge, ruled in their favor, stating that it is unlikely that Mr. Grünbaum voluntarily donated the artworks while detained at Dachau.

According to prosecutors, this prompted Mr. Grünbaum's successors to escalate their case to the Manhattan district attorney to determine whether other Schiele works once owned by Mr. Grünbaum qualify as stolen property under New York law.

By doing so, prosecutors were able to trace how the seven artifacts entered various collections in New York. Timothy Reif, a relative of Mr. Grünbaum, praised the role that New York prosecutors played in returning the artworks to their rightful proprietors.

Mr. Reif stated on Monday that the recovery "achieved some measure of justice for the homicide and robbery victims." Among the artworks returned is a piece titled I Love Antithesis, valued at $2.75 million and Standing Woman, formerly on exhibit at the MoMA, valued at $1.5 million.

The return of these works followed last week's notification by Manhattan prosecutors of their intention to seize three additional works of art from galleries in Chicago, Pittsburgh, and Ohio.

According to the state supreme court of New York, there is reasonable cause to believe that the artworks constitute seized property.

For the time being, the artifacts remain in the museums, whose representatives have expressed confidence in their legal ownership. A federal proceeding is currently underway to resolve the matter.