Preparing for the exhibition took four years. Mr. Groeneweg and other curators researched Mata Hari’s past extensively and drew new conclusions about her history. It was not entirely clear that she ever spied for the Germans, for example, though she admitted to taking money from them, perhaps because she was broke at the time. “When you read what information she gave to the Germans, you think it’s all very small,” Mr. Groeneweg said. “Like she’d tell that there was going to be an offensive in the spring, but everyone already knew that.” The exhibition presents original documents from her trial — including her “confession” document — that were unsealed by the French authorities in January, along with personal letters and diary entries, on loan from Zelle’s family, that have never been shown to the public.