Dutch systems specialist Paul Post had glimpsed the notebooks that contained his father’s Nazi-era diaries before, but when he rediscovered them in an attic 15 years ago, the recent retiree finally had time to closely examine them. Post, 74, had no idea that they would ultimately lead to Argentina, where in September the daughter of a high-ranking Nazi official was charged with concealing an 18th-century painting looted during the Holocaust. In his diaries, Post’s father described working in the Netherlands' diamond bureau when it was taken over by the Nazis.

As Post began researching the events, one name jumped out: the Nazi official Friedrich Kadgien. Kadgien oversaw the Nazi looting of diamonds and gold from occupied countries. Post began to follow Kadgien’s wanderings after the war, hoping to solve the mystery of the diamonds that historians say are still missing. He learned by chance that Kadgien was believed to have also possessed looted art. The hunt led him and Dutch journalists to the peaceful residential neighborhood home of Patricia Kadgien, 60, in the seaside town of Mar del Plata in Buenos Aires province, where "Portrait of a Lady” had been hanging prominently in her living room. The reporters spotted it in a real estate listing in August. Her attorney, Carlos Murias, said she did not know about claims the painting had been looted from the collection of Jewish art dealer Jacques Goudstikker and she has denied having hidden it. Nazi-related discoveries like this occasionally pop up in Argentina, which after the war received both Holocaust survivors and dozens of Nazi war criminals, including Adolf Eichmann and Josef Mengele.