He bought the Leefsmas’ painting, which would remain in the Dutch museum for the next 57 years until its return to the heirs of the family in 2000. In five other cases, the museum settled restitution claims by returning works acquired during Mr. Hannema’s reign as director from 1921 to 1945.

“He collaborated with the Germans and he knew what he was doing,” Sjarel Ex, the current director of the museum, said of his predecessor. “His decision was that it was worthwhile to work with them because he knew that he could have more influence and power with the people who were reigning instead of being a refugee or going into hiding or living on the outskirts.”

Though Mr. Hannema’s relationship with the Germans has been previously recognized by historians, the details of his collaboration are being revisited these days as part of a sweeping review by Dutch museums of their war-era record. In a recent report, the Netherlands Museum Association announced that after a decade of research, Dutch museums have so far discovered 172 artworks in their collections with problematic histories, suggesting they may have been looted or sold under duress. Thirty of those works are in the Boijmans collection, though museum officials say they were acquired after Mr. Hannema left as director.

Across Europe, museums are still grappling — some more diligently than others — with how to identify and handle works of art that may have a tainted wartime history. The Dutch drive gained significant momentum in the late 1990s, though the process has moved forward since in fits and starts. The research has expanded over time to include not just art acquired by museums before or during the war, but also gifts that came later that have suspicious gaps in their provenance.

This year as part of the renewed research efforts, the Boijmans, now known as the Museum Boijmans Van Beuningen, supplemented its inventory process with a separate report by an independent historian, plus an exhibition, “The Boijmans in the War. Art in a Destroyed City,” that discusses Mr. Hannema’s role. The museum director’s life is also the subject of a new biography by the Dutch art and cultural historian Wessel Krul, which was published last month.